DTU ProjectLab - User contributions [en-gb]

The Critical Path Method (CPM)

2015-09-28T09:34:25Z

Sissel:

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="48%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>. Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:33:04Z

Sissel:

The Critical Path Method (CPM)

2015-09-28T09:29:37Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="48%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated

project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:26:24Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated

project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:25:41Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated

project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:23:59Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated

project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated. {{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:23:11Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated

project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated. {{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:21:39Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated. {{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:19:49Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:18:26Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:17:16Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:16:24Z

Sissel: /* Limitations */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:14:16Z

Sissel:

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:12:56Z

Sissel: /* Guidance on use */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:11:36Z

Sissel: /* Insuring time schedule */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:11:05Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:08:41Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos'''
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:06:49Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="66%" {| class="wikitable" width="66%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
===Articles===
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

===Videos===
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

===Books===
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

===Links===
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:05:31Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="68%" {| class="wikitable" width="68%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
===Articles===
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

===Videos===
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

===Books===
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

===Links===
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:05:10Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
===Articles===
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

===Videos===
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

===Books===
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

===Links===
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:04:52Z

Sissel: /* Articles */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
===Articles===
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

===Videos===
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

===Books===
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

===Links===
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:04:27Z

Sissel: /* Articles */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
===Articles===
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

===Videos===
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

===Books===
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

===Links===
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:04:09Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
===Articles===
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

===Videos=== 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

===Books===
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

===Links===
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:03:09Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 
'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:01:30Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined (Table 1).

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T09:00:18Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]
'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T08:55:32Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="65%" {| class="wikitable" width="65%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T08:55:04Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="60%" {| class="wikitable" width="60%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.
{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}

'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T08:29:42Z

Sissel: /* Tool and method */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="60%" {| class="wikitable" width="60%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-28T08:28:21Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

Talk:The Critical Path Method (CPM)

2015-09-27T18:16:48Z

Sissel:

Anna:
Very nice topic that focuses on a specific tool.
It seems that you have a good grasp on the structure and that you will follow the requirements stated.

'''Review 2, Nannats''' 
Hi s112195 :-)

* I think it is nice that you have linked to some of the other wiki articles – you are good at doing that through the entire article :-)
* I think that the language through the article is good, and easy to understand.
* In my opinion, the section ‘Guidance on use’, is long and with a lot of text. You could consider making a subsection with either the ‘challenges’ that you mention or the ‘Fast Tracking or Crashing’ part.
* In my point of view, I miss something (maybe a guidance) on how to find the critical path, maybe with an example. The section with the ‘Tool and Method’ does not quite seem to be finish?
* The discussion part on the limitations is good, it seems like you touch a lot of different aspects.
* Under ‘Additional reading’ you write something about ''"more information on the Cynefin Framework"'' – I think that must be a mistake? :-)

Overall, a nice article, so good job :-)

'''To: Review 2''' 
Thank you for your very nice words about by article. I did decide to add sections to "guidance on use" and it helped get a better structure of the article. I also wrote a better and longer explanation on how the find the critical path. Thanks you again, your comments were useful.

'''s103183, Reviewer 1:'''

*'''!!!!!I Made this review just before class today, but just noticed that a lot has changed since then!!!!!'''
* I like the overall structure of the article and the introduction and that the introduction to CPM is no to detailed and hard to follow.
* The first thing I notice however is that the article is not yet finished as several parts are missing.
* A good thing is that you seem to have a lot of different references which shows that you have reseached the topic even though the article is far from finished.
* I would recommend to put in an example of how to use it or somehow show how to use the method when you finish the article.
* An idea could be to give a short description of the additional reading, what it contains etc.
* As a last comment I would recommend to change the text in the ”Additional reading part” from ”the Cynefin Framework” to something like ”The Critical Path Method”.

'''To: Review 1''' 
Unfortunately I couldn’t use your comments, because I already had made most of the article but first uploaded it short before the class started. All of your comments were already included. Thank you anyway.

'''S113815, Review 3. [1985 words]'''

Dear s112195.

After reviewing your article, I have following comments:

First of all, I think the article is consistently well-written and explains a tool which is very useful in the field of project management. There structure of the article seems to follow the guidelines from the assignment. There is a red thread throughout the article and the examples is easy to understand.

I have made some comments and tried to make some suggestions to make the article even better, they are as followed:

'''Summary'''
* ..” With available accurate task time estimate CPM is the preferred method.” Says who? Do you have references to back up this statement?
* I like your links to the internal Wiki-articles. Thus, the link to PERT is not connected to a wiki-article?
* Overall a good paragraph that sums up the tool.

'''Introduction to CPM'''
*Really well-written paragraph.
* My only comment is to the links you have made. All the links is to the internal wiki-page. On this page, there is no article on Microsoft Project etc. Therefore, you might change these links to the “real” Wikipedia.

'''Tool and method'''
* Nice figures. Thus, the figures are missing figure number and the big one is also missing figure text.
* There is no cross reference from the text to the figures. I think it would be nice if the figures were used to support the key points in the text. E.g. “Bla bla bla, is illustrated in figure x”. :)
* I feel the figure in the middle needs a little more explanation. It is a little hard to follow. Maybe an example from real-life project could be used?

'''Guidance on use'''
* Again, a very well written paragraph.
* “The most logical and efficient way to work is on one project at the time, unfortunately this is almost never the case.” Should it be “… to work is one task at the time,…”? Not project?
* If fell like the paragraph tells a lot about why I should use CMP and who I can benefit from using it. I miss the “aha” feeling. After reading “guidance on use” I still don’t think I would be able to use the tool right away. I would suggest a more practical “hands-on” example to give the reader a specific way to use the tool.

'''Discussion on limitations'''
* “A schedule created from CPM involves a lot of fluctuation because you have to use best-guess estimates to calculate time.” Very nice point!
* I like the discussion between manual vs. computer work.
* In my opinion, the best paragraph in the article!

'''Conclusion, Additional reading, Bibliography'''
* All three sections looks nice in form of format.
* There are missing authors in some of the references in the bibliography
* The videos are a little misplaced on the page. I would suggest to put them under each reference. (But nice touch with the videos – Super! )
* The second reference in bibliography has a fail: “↑ name="Sm15"”

'''General to the article'''
* I didn’t find any typing errors or crucial grammatical errors – nice work.
* I like the amount of links in your article. Thus, some of them are linking to unexcisting wiki-pages. Maybe these should be changes to the “real” Wikipedia?
* As you still have 1000 words to use, you might consider adding an example to strengthen your theory.

All in all a very nice article – and good work. :)

'''To: Review 3''' 
Thank you for your nice words about the article.
I thought the references to other wiki articles were working. Thanks for letting me know, so I could correct my mistake and add references to “real” Wikipedia site. References to pictures are now made, well spotted. I have included more to the paragraph “guidance to use”, so I think you will get the Ahha feeling now  Thank you for the many recommendations, I have used many of them and it made my article better for sure.

Talk:The Critical Path Method (CPM)

2015-09-27T18:15:34Z

Sissel:

Anna:
Very nice topic that focuses on a specific tool.
It seems that you have a good grasp on the structure and that you will follow the requirements stated.

'''Review 2, Nannats''' 
Hi s112195 :-)

* I think it is nice that you have linked to some of the other wiki articles – you are good at doing that through the entire article :-)
* I think that the language through the article is good, and easy to understand.
* In my opinion, the section ‘Guidance on use’, is long and with a lot of text. You could consider making a subsection with either the ‘challenges’ that you mention or the ‘Fast Tracking or Crashing’ part.
* In my point of view, I miss something (maybe a guidance) on how to find the critical path, maybe with an example. The section with the ‘Tool and Method’ does not quite seem to be finish?
* The discussion part on the limitations is good, it seems like you touch a lot of different aspects.
* Under ‘Additional reading’ you write something about ''"more information on the Cynefin Framework"'' – I think that must be a mistake? :-)

Overall, a nice article, so good job :-)

'''To: Review 2''' 
Thank you for your comments. I did decide to add sections to "guidance on use" and it helped get a better structure of the article. I also wrote a better and longer explanation on how the find the critical path. Thanks your comments were useful.

'''s103183, Reviewer 1:'''

*'''!!!!!I Made this review just before class today, but just noticed that a lot has changed since then!!!!!'''
* I like the overall structure of the article and the introduction and that the introduction to CPM is no to detailed and hard to follow.
* The first thing I notice however is that the article is not yet finished as several parts are missing.
* A good thing is that you seem to have a lot of different references which shows that you have reseached the topic even though the article is far from finished.
* I would recommend to put in an example of how to use it or somehow show how to use the method when you finish the article.
* An idea could be to give a short description of the additional reading, what it contains etc.
* As a last comment I would recommend to change the text in the ”Additional reading part” from ”the Cynefin Framework” to something like ”The Critical Path Method”.

'''To: Review 1''' 
Unfortunately I couldn’t use your comments, because I already had made most of the article but first uploaded it short before the class started. All of your comments were already included. Thank you anyway.

'''S113815, Review 3. [1985 words]'''

Dear s112195.

After reviewing your article, I have following comments:

First of all, I think the article is consistently well-written and explains a tool which is very useful in the field of project management. There structure of the article seems to follow the guidelines from the assignment. There is a red thread throughout the article and the examples is easy to understand.

I have made some comments and tried to make some suggestions to make the article even better, they are as followed:

'''Summary'''
* ..” With available accurate task time estimate CPM is the preferred method.” Says who? Do you have references to back up this statement?
* I like your links to the internal Wiki-articles. Thus, the link to PERT is not connected to a wiki-article?
* Overall a good paragraph that sums up the tool.

'''Introduction to CPM'''
*Really well-written paragraph.
* My only comment is to the links you have made. All the links is to the internal wiki-page. On this page, there is no article on Microsoft Project etc. Therefore, you might change these links to the “real” Wikipedia.

'''Tool and method'''
* Nice figures. Thus, the figures are missing figure number and the big one is also missing figure text.
* There is no cross reference from the text to the figures. I think it would be nice if the figures were used to support the key points in the text. E.g. “Bla bla bla, is illustrated in figure x”. :)
* I feel the figure in the middle needs a little more explanation. It is a little hard to follow. Maybe an example from real-life project could be used?

'''Guidance on use'''
* Again, a very well written paragraph.
* “The most logical and efficient way to work is on one project at the time, unfortunately this is almost never the case.” Should it be “… to work is one task at the time,…”? Not project?
* If fell like the paragraph tells a lot about why I should use CMP and who I can benefit from using it. I miss the “aha” feeling. After reading “guidance on use” I still don’t think I would be able to use the tool right away. I would suggest a more practical “hands-on” example to give the reader a specific way to use the tool.

'''Discussion on limitations'''
* “A schedule created from CPM involves a lot of fluctuation because you have to use best-guess estimates to calculate time.” Very nice point!
* I like the discussion between manual vs. computer work.
* In my opinion, the best paragraph in the article!

'''Conclusion, Additional reading, Bibliography'''
* All three sections looks nice in form of format.
* There are missing authors in some of the references in the bibliography
* The videos are a little misplaced on the page. I would suggest to put them under each reference. (But nice touch with the videos – Super! )
* The second reference in bibliography has a fail: “↑ name="Sm15"”

'''General to the article'''
* I didn’t find any typing errors or crucial grammatical errors – nice work.
* I like the amount of links in your article. Thus, some of them are linking to unexcisting wiki-pages. Maybe these should be changes to the “real” Wikipedia?
* As you still have 1000 words to use, you might consider adding an example to strengthen your theory.

All in all a very nice article – and good work. :)

'''To: Review 3''' 
Thank you for your nice words about the article.
I thought the references to other wiki articles were working. Thanks for letting me know, so I could correct my mistake and add references to “real” Wikipedia site. References to pictures are now made, well spotted. I have included more to the paragraph “guidance to use”, so I think you will get the Ahha feeling now  Thank you for the many recommendations, I have used many of them and it made my article better for sure.

Talk:The Critical Path Method (CPM)

2015-09-27T18:06:28Z

Sissel:

Anna:
Very nice topic that focuses on a specific tool.
It seems that you have a good grasp on the structure and that you will follow the requirements stated.

'''Review 2, Nannats''' 
Hi s112195 :-)

* I think it is nice that you have linked to some of the other wiki articles – you are good at doing that through the entire article :-)
* I think that the language through the article is good, and easy to understand.
* In my opinion, the section ‘Guidance on use’, is long and with a lot of text. You could consider making a subsection with either the ‘challenges’ that you mention or the ‘Fast Tracking or Crashing’ part.
* In my point of view, I miss something (maybe a guidance) on how to find the critical path, maybe with an example. The section with the ‘Tool and Method’ does not quite seem to be finish?
* The discussion part on the limitations is good, it seems like you touch a lot of different aspects.
* Under ‘Additional reading’ you write something about ''"more information on the Cynefin Framework"'' – I think that must be a mistake? :-)

Overall, a nice article, so good job :-)

'''To: Review 2''' 
Thank you for your comments. I did decide to add sections to "guidance on use" and it helped get a better structure of the article. I also wrote a better and longer explanation on how the find the critical path. Thanks your comments were useful.

'''s103183, Reviewer 1:'''

*'''!!!!!I Made this review just before class today, but just noticed that a lot has changed since then!!!!!'''
* I like the overall structure of the article and the introduction and that the introduction to CPM is no to detailed and hard to follow.
* The first thing I notice however is that the article is not yet finished as several parts are missing.
* A good thing is that you seem to have a lot of different references which shows that you have reseached the topic even though the article is far from finished.
* I would recommend to put in an example of how to use it or somehow show how to use the method when you finish the article.
* An idea could be to give a short description of the additional reading, what it contains etc.
* As a last comment I would recommend to change the text in the ”Additional reading part” from ”the Cynefin Framework” to something like ”The Critical Path Method”.

'''To: Review 1''' 
Unfortunately I couldn’t use your comments, because I already had made most of the article but first uploaded it short before the class started. All of your comments were already included. Thank you anyway.

'''S113815, Review 3. [1985 words]'''

Dear s112195.

After reviewing your article, I have following comments:

First of all, I think the article is consistently well-written and explains a tool which is very useful in the field of project management. There structure of the article seems to follow the guidelines from the assignment. There is a red thread throughout the article and the examples is easy to understand.

I have made some comments and tried to make some suggestions to make the article even better, they are as followed:

'''Summary'''
* ..” With available accurate task time estimate CPM is the preferred method.” Says who? Do you have references to back up this statement?
* I like your links to the internal Wiki-articles. Thus, the link to PERT is not connected to a wiki-article?
* Overall a good paragraph that sums up the tool.

'''Introduction to CPM'''
*Really well-written paragraph.
* My only comment is to the links you have made. All the links is to the internal wiki-page. On this page, there is no article on Microsoft Project etc. Therefore, you might change these links to the “real” Wikipedia.

'''Tool and method'''
* Nice figures. Thus, the figures are missing figure number and the big one is also missing figure text.
* There is no cross reference from the text to the figures. I think it would be nice if the figures were used to support the key points in the text. E.g. “Bla bla bla, is illustrated in figure x”. :)
* I feel the figure in the middle needs a little more explanation. It is a little hard to follow. Maybe an example from real-life project could be used?

'''Guidance on use'''
* Again, a very well written paragraph.
* “The most logical and efficient way to work is on one project at the time, unfortunately this is almost never the case.” Should it be “… to work is one task at the time,…”? Not project?
* If fell like the paragraph tells a lot about why I should use CMP and who I can benefit from using it. I miss the “aha” feeling. After reading “guidance on use” I still don’t think I would be able to use the tool right away. I would suggest a more practical “hands-on” example to give the reader a specific way to use the tool.

'''Discussion on limitations'''
* “A schedule created from CPM involves a lot of fluctuation because you have to use best-guess estimates to calculate time.” Very nice point!
* I like the discussion between manual vs. computer work.
* In my opinion, the best paragraph in the article!

'''Conclusion, Additional reading, Bibliography'''
* All three sections looks nice in form of format.
* There are missing authors in some of the references in the bibliography
* The videos are a little misplaced on the page. I would suggest to put them under each reference. (But nice touch with the videos – Super! )
* The second reference in bibliography has a fail: “↑ name="Sm15"”

'''General to the article'''
* I didn’t find any typing errors or crucial grammatical errors – nice work.
* I like the amount of links in your article. Thus, some of them are linking to unexcisting wiki-pages. Maybe these should be changes to the “real” Wikipedia?
* As you still have 1000 words to use, you might consider adding an example to strengthen your theory.

All in all a very nice article – and good work. :)

The Critical Path Method (CPM)

2015-09-27T17:57:50Z

Sissel: /* Insuring time schedule */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence<ref name="Rob"/>.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:57:21Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:56:37Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.
*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.
*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:51:26Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:50:54Z

Sissel: /* Additional reading */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides clear and thorough information about the basis of a Gantt chart, how to preform a Gantt Chart, individual features and how it can be used in management.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}
*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}
*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:46:08Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:43:53Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path.
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks.

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations. Moreover CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:41:25Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of projects furthermore it is easy to comprehend and to use.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path.
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks.

CPM often provides a better understanding than the conventional bar chart, because it illustrates relationships that controls the order of performance in the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore identifyed slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory. Specialized computerized methods to calculate the critical path have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations.

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has to be on securing accurate duration time.

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:30:24Z

Sissel: /* Time estimates */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects furthermore it is easy to comprehend and to use.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path.
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks.

Specialized computerized methods to calculate critical path ways have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations.
CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has to be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T17:29:13Z

Sissel: /* Limitations */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that focus on the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects furthermore it is easy to comprehend and to use.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path.
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks.

Specialized computerized methods to calculate critical path ways have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations.
CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has to be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:51:25Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that factor in the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects furthermore it is easy to comprehend and to use.

A challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path.
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks.

Specialized computerized methods to calculate critical path ways have been developed.
Especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations.
CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
The knowledge of the operational flow can be used for resource allocation and equipment requirement estimates. Furthermore slack time can be used to optimize resource allocation.
A manually calculated and drawn CPM diagrams is easy to perform and gives a good overview of the project. With more complicated project the need for computer programs are mandatory.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has to be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:42:42Z

Sissel: /* Conclusion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that factor in the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Tasks which have slack time
*Resources allocation needed to achieve a project
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has to be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:39:12Z

Sissel: /* Limitations */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that factor in the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

===Time estimates===
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

===Computer programs===
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Resources needed to achieve a project
*Tasks which have slack time
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:37:48Z

Sissel:

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that factor in the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

'''Time estimates'''
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.<ref name="CAP15"/>

One way to overcome this issue is by applying the CCM. By diminishing the task time estimate with 50% you also minimizes the possible error estimate and by introducing the buffer time you have a pool of time to be spend when needed. Moreover the buffer time gives you a way of continuously overlooking the project schedule<ref name="Bell"/>.

'''Computer programs'''
As projects often tend to be complex having several critical paths and change of the critical paths during the project, CPM can sometimes be difficult to use and understand. To overcome this challenge specialized computerized methods to calculate critical path have been developed. An example of this is the Linear Scheduling Model<ref name="Yam01"/>.

The advantages of the manual method compared with using the computer method is, that it overcomes certain weaknesses which result from the assumption that each operation in the project is independent of every other operation, except for the sequential relationship shown by the network chart. Furthermore it is impractical to exert intermediate control over the calculations to recognize changes in input data or related effects between operations with the computer method. On the other hand especially with long duration projects where the critical path will change often it is highly applicable with computerized methods being capable of new fast calculations<ref name="Fon62"/>.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Resources needed to achieve a project
*Tasks which have slack time
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:33:04Z

Sissel: /* Limitations */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that factor in the risks caused by dependence on unique or constrained resources<ref name="KEN"/>.

'''Time estimates'''
CPM needs only one time estimate per task, this makes it easy to handle but more inaccurate, compared to the PERT method, which is dependent on three time estimates per task (earliest, latest, average).
A schedule created from CPM involves risk of fluctuation because it is based on best guess estimates to calculate time. CPM is therefore only as powerful as the estimates entered into it. If the estimations are off or if the resources are not calculated correctly, the critical path could change and a delay will happen in worse case it may cause an entire project to fail.

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Resources needed to achieve a project
*Tasks which have slack time
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:31:09Z

Sissel: /* Limitations */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==
A limitation of CPM is that it highlights tasks at greatest risk for causing schedule delays, but it does not identify the source of the schedule risks. Different methods, such as the Critical Resource Path Technique identified by Aguanno (2002) calculate alternate critical paths that factor in the risks caused by dependence on unique or constrained resources

(KILDE)

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Resources needed to achieve a project
*Tasks which have slack time
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>

The Critical Path Method (CPM)

2015-09-27T16:08:52Z

Sissel: /* Discussion */

[[Category:Project Management]][[Category:Method artikel]][[Category:Management]][[Category:Critical Chain Theory]]
This method article describes the Critical Path Method (CPM) also in comparison to other project management methods. This article describes how and when to use CPM methods, moreover discusses the advantages, disadvantages and applicability of the method. CPM is a step-by-step project management method for process planning. CPM was developed in 1956 by the E.I. du Pont de Nemours Company a major chemical plant construction firm in USA<ref name="Woodhead"/>. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project and helps define the most critical tasks that needs to be accelerate in order to complete the project within the available time. Furthermore CPM can be used to monitor if the project follows the time schedule and it allows you to identify slack time (free resources)<ref name="Ver09"/>.
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects<ref name="Fon62"/>.

==Introduction to CPM==
CPM is a step-by-step method for project planning and management. It is the presentation of a project plan by a schematic diagram that depicts the sequence and interaction of all the tasks of the project<ref name="Woodhead"/>. The precursor of CPM was PERT (Program, Evaluation, Review and Technique) and PPS (Project Planning and Scheduling) developed by the U.S. Navy. PERT uses three time estimates (earliest, latest, average) to define the total project duration time, so less acurate time estimates can be used in this method. PPS focus on estimates on both cost and time for design, construction and maintenance work <ref name="Woodhead"/>.

The main benefits of CPM for the projects managers are primarily to identify the most important tasks. By focusing on tasks duration CPM identifies the minimum length of time needed to complete a project, this is based on identifying the critical path. If any of the tasks forming the critical path take more time than their estimated durations, start or finish later than planned, then the whole project will be affected. The critical path is by the Project Management Body of Knowledge (PMBOK), an internationally recognized collection of processes and knowledge areas accepted as best practice for the project management profession. It is defined as ''“the sequence of scheduled activities that determines the duration of the project”''. The critical path helps define the most efficient way to schedule the project. Although many projects have only one critical path, some projects may have multiple critical paths.

Secondly, CPM helps reduce timelines by identifying slack time. Slack time tells to what extent each activity in the schedule can slip (float) without delaying the project<ref name="Sm15"/>.

In the early stage of CPM there was not any computer programs to make the calculations and the network diagrams was made using hand drawn nodes to present the stages of a product. Today there are a number of project management software programs available that can do the calculation. [https://da.wikipedia.org/wiki/Microsoft_Project Microsoft Project] and [https://en.wikipedia.org/wiki/Smartsheet Smartsheet] are two different computerized tools that use CPM<ref name="Sm15"/>.

==Tool and method==
{| style=class="wikitable" width="50%" {| class="wikitable" width="48%" {| class="wikitable" style="float:right; margin-left: 10px;"
|+ '''Table 1:''' Details of critical path<ref name="DrP11"/>
! style="background:#d0e5f5" | ''' Activity '''
! style="background:#d0e5f5" | ''' Predecessor'''
! style="background:#d0e5f5" | ''' Duration (weeks)'''

|-
| style="text-align:center;"| A
| style="text-align:center;"| -
| style="text-align:center;"| 2
|-

| style="text-align:center;"| B
| style="text-align:center;"| A
| style="text-align:center;"| 3
|-

| style="text-align:center;"| C
| style="text-align:center;"| B
| style="text-align:center;"| 1
|-

| style="text-align:center;"| D
| style="text-align:center;"| A
| style="text-align:center;"| 6
|-

| style="text-align:center;"| E
| style="text-align:center;"| C , D
| style="text-align:center;"| 3
|-
|}

CPM is still an incredibly important tool to project managers, even though it is almost 60 years old. It provides a visual representation of project activities and clearly presents the time required to complete tasks.
Construction of a CPM can be subdivided into four phases.

'''Phase 1''': The construction of a sequential relationship of the individual operations in the project where each task is named and defined.

[[File:Precedence_Diagram.PNG‎|450px|thumb|right|'''picture 1:''' Precedence Diagram]]
'''Phase 2''': The construction of a sequential schedule called a Precedence Diagram (Picture 1). The Precedence Diagram depicting their sequential relationship.

[[File:Aktivity_Identity_box3.PNG|450px|thumb|right|'''Picture 2:''' Aktivity Identity box]]
'''Phase 3''':The construction of the Activity Identity boxes (Picture 2). Each task has an Activity Identity Box which contains information regarding task name, duration, early start, early finish, late finish, late start and slack time. The completion of the Activity Identity Boxes is carried out by filling in task name and duration, furthermore performing firstly a forward pass (early start, early finish) and backward pass (late finish, late start and slack time)<ref name="DrP11"/>.

[[File:CMP_diagram_calculations.PNG|450px|thumb|right|'''Picture 3:''' CPM Diagram calculatoins, Including forward pass shows minimal time use (from left to right) and backward pass shows maximal time use (from right to left)]]

[[File:CMP_diagram.PNG‎|450px|thumb|right|'''Picture 4:''' CPM Diagram including
Critical path which is the longest duration time (red arrows) and slack time which is free resources (green boxes)]]

'''Phase 4''':The CPM path diagram can be completed and the critical activities determining the overall project duration can be identified (Picture 3). The critical path is identified as the path with the longest duration time e.i. the fastest time the project can be finish. In the example (Picture 3) the critical path shown with the red arrow is A, D and E because the duration time 11 weeks is longer compared to 9 weeks for A, B, C and E.
Furthermore slack time for the individual activities can be calculated either thought Late Finish minus Early Finish or Late Start minus Early Start (Picture 4)<ref name="Fon62"/>.

==Guidance on use==
CPM is one of the fundamental concepts in traditional project management. Especially by construction contractors it can be applied for the planning, scheduling and control of construction projects. CPM produces a planned schedule to guide the project team, and it forms the basis for tracking project schedule performance by comparing actual with planned task progress. In a project with lots of tasks and dependencies it can be difficult to identify the most critical tasks that, if missed, will impact the whole project. CPM identifies this/these critical tasks and can be used to evaluate whether the project stay on track or not.<ref name="Sm15"/>

===Insuring time schedule===
The project manager has difficulties in estimating the exact duration for a project. This is caused by both CPM being based on the uncertain estimated task duration time and occurrence of unexpected factors which may impact tasks completion. Considerations needs to be made to minimise the effect of unexpected factors<ref name="Sm15"/>.

Using the CPM the project manager may realize that he needs to compress the project schedule. There is two way of solving the issue either Fast Tracking or Crashing.

'''Fast Tracking'''
In Fast Tracking the project manager searches for activities from the critical path that can be done parallel to each other, in order to move the project along faster. The reason to look only on tasks from the critical path is because all the other activities have slack time and having them finishing early is only going to give more slack time. While fast tracking reduces the project timeframe. It also involves risk because you are performing parallel activities that were originally planned to be performed in sequence.

'''Crashing'''
Crashing is the other way of compressing or shorting down a project. Here the project manager identifies the shortest possible time for which a task can be scheduled when adding the necessary resources. By speeding up the processes there is a risk of lower quality of work<ref name="Sm15"/>.

===The precusor to Gantt Chart===
A [[Gantt Chart]] is a commonly used tool within project management, which, briefly, shows the progress of an ongoing project.The chart shows the tasks that need to be done in a project, when each task needs to be performed, and how long time they are going to take according to the plan<ref name="Orr03"/>. The critical path identified by the CPM is often used as a precursor to Gantt Charts<ref name="Fon62"/>.

===Constrain issue===
When managing a project with CPM you are focusing on the critical path. An unexpected event might change the critical path and a consequence could be resource constraint issues. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities and resource leveling. When the tasks on the critical path are affected by resource constraints the previously shorter path could become the longest or most “resource critical” path<ref name="Sm15"/>.

===Comparison of work programs, construction methods and equipments===
CPM permits comparison of alternative work programs, construction methods and equipments. CPM provides the projects manager with precise information on the effects of each variation or delay in the adopted plan and thereby indicates where to have the main focus to stay on time. Furthermore CPM allows you to identify slack time and helps you to secure that the project follows the time schedule<ref name="Woodhead"/>.

===Critical chain management===
A new and more efficient way of utilizing the CPM is in the Critical Chain Management (CCM). CCM has five basic conditions (no milestones, no multitasking, no reporting of early completions of tasks, individual estimates of task duration is reduced with 50 %, buffer time is introduced).
The task time estimate is minimised with 50 % in the critical chain management.This is compensated for by introduction of the buffer time. Further the buffer time are used as a warning mechanism during project schedule execution. If more than 66% of the buffer have been used then actions needs to be made<ref name="Bell"/>.

==Discussion==
CPM is a project planning, managing and scheduling method which is easy to comprehend and to use. This is caused by the step-by-step method and the presentation of the project in an easy comprehensible schedule diagram, depicting both the sequence, duration and the interaction of all the tasks in the given project<ref name="Woodhead"/>.

As a project manager it is mandatory for you continually to able to track the progress in the project. There are four different way to track the progress, either by using CPM, Gantt Chart, Critical Chain Management or PERT.
Gantt Chart has the advantages of being able to evaluate the flow of the project on daily or weekly basis compared to CPM that can only check the progress of each finalised task. CPM often provides a better understanding than the conventional bar chart, because it illustrates relationship that controls the order of performance of the various operations.
Critical Chain Management on the other hand follow the progress by looking at the buffer time. Moreover a challenge with the CPM is not to lose sight of the risks inherent in tasks not on the critical path. This might happen because of the extra attention the critical path requires. The completion of a task not on the critical path could be delayed, this could cause that the duration time becomes long enough to change the critical path of the project.
There are two methods by which you can identify the critical path through the project. Either CPM as described above or PERT. PERT is used in projects with inaccurate time estimates by applying three time estimates to create the expected time duration for the project. With available accurate task time estimate CPM is the preferred method. CPM is the most simplified method and are therefore the preferred method<ref name="DrP11"/>.

CPM can be used to increase the effectiveness of a given project. Scheduling certain activities at the same time, might lead to a need of more people than there are available. A solution to this is to reschedule the activities. By identifying slack time it is possible to reallocate resources from tasks with slack to the critical tasks. Thereby being more efficient and securing timely completion.

By comparing alternative work programs, construction methods and equipments CPM can help evaluate which method is the most efficient. Each of the changes can be evaluatedseparately with CPM. The specific change can be placed in either the Precedence Diagram or in the Activity Identity box after which the CPM Diagram can be completed and the critical tasks can be determined to calculate the overall duration time<ref name="DrP11"/>.

The handmade CPM is fast to make for relatively simple projects and a god the manager can get a good overview of the tasks importance with the CPM Diagram but it is not as easy with bigger or more complicated projects. Here the computerization can be useful. It requires training to use and money to obtain, but can easy manage complex projects with multiple critical paths. Furthermore, the computerized CPM can quickly calculate new critical paths when a change occurs<ref name="Sm15"/>.

==Limitations==

==Conclusion==
CPM is one of the fundamental concepts in traditional project management. CPM utilizes tasks duration as the parameter for optimization of the schedule, resource planning and control of construction projects.

CPM is an effective and powerful method of assessing:
*The shortest time in which a project can be completed
*Task priorities
*The most critical tasks
*Resources needed to achieve a project
*Tasks which have slack time
*The sequence of activities, scheduling, and timings involved

Furthermore CPM provides a mechanism for determining all of the operations affected by a given change as well as the effect on project duration. It provides the mechanism for determine the least cost to compress project completion time. To use CPM optimal focus has be on securing accurate duration time

==Additional reading==
For more information on the Critical Path Method, you might find the following sources useful 

'''Articles'''
*'''Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001)''': 127(5), 374-381. <ref name="Yam01">Yamin R. & Harmelink. "Comparison of Linear Scheduling Model (LSM) and Critical Path Method (CPM)." J. Constr. Eng. Manage (2001): 127(5), 374-381.</ref>This is a technical paper by René A. Yamín and David J. Harmelink in cooperation with Journal of Construction Engineering and Management about differences and similarities between the two models Linear Scheduling and Critical Path.

*'''Aguanno, Kevin . "Critical Path: An Extended Definition." MMPUBS.com (2002)'''. <ref name="KEN">Aguanno, Kevin. "Critical Path: An Extended Definition." MMPUBS (2002).</ref>This is a five pages long artikel by Senior Project Manager, Kevin Aguanno. It describes history, definitions, limitations, alternatives and behind the Critical Path.

*'''Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003)'''. <ref name="Orr03">Orr, Alan. "Uncharted Territory?". Engineering Management Journal. (2003).</ref>This is an article written by Alan Oro, and is written for a journal called Engineering Management Journal. It provides really good information about the basis of a Gantt chart, like how is it made, which features does it have, and how to use it.

'''Books'''
*'''Woodhead, James M. Antill & Ronald W. "Critical Path Methods in Construction Practice". John Wiley & Sons, Inc. (1990)'''. <ref name="Woodhead"> Woodhead, James M. Antill & Ronald W."Critical Path Methods in Construction Practice" John Wiley & Sons, Inc. (1990).</ref>This is an "old" book from 1990. The descriptions of the Critical Path Method is very clarifying and detailed.
*'''Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962)'''. <ref name="Fon62">Fondahl, John W. "A non-computer approach to the critical path method for the construction". Stanford University. (1962).</ref>This book is mad incoorporation with the department of civil engineering og Standford University by Jown W. Fondahl a professor of Civil Engineering. The preparation for this book is made under a research contract by the U.S. Navy. It contains the CPM approach and history. Because of its age the section about future implications it outdated.

'''Links'''
*'''Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)''': http://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article <ref name="Ver09">Verma, Eshna. "What is Critical Chain Project Management?". Simplilearn (2009)</ref>This link gives a good overview of the Critical Chain Project Management Method. It is written by Eshna Verma is a writer at Simplilearn.
*'''Burger, Rachel. "The Secret to the Critical Path Method in Construction". Capterra (2015)''': http://blog.capterra.com/construction-critical-path-method/<ref name="CAP15">Burger, Rachel. "The Secret to the Critical Path Method in Constructio" (2015)</ref>A Simpel artikel the Critical Path Method with focus on how to use is in construction. It is very basic and foreseeable.
*'''Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". Smartsheet (2015)''': https://www.smartsheet.com/critical-path-method/<ref name="Sm15">Dr. Larry Bennett. "The Ultimate Guide to the Critical Path Method". (2015)</ref>This is a good link with general informaiton about CPM, background, history, everyday advantages, key steps and comparrison with other methods. This link includes several good youtube clips made by the author Dr. Larry Bennett, a civil engineer, project manager, and author of four books, including a guide on critical path written in 1978. It also cantains multible comments from others with knowledge about CPM.

{{#ev:youtube|www.youtube.com/watch?v=DdDzybQ_9vM|200|right|Critical Path Method and PERT explained by Dr. Pamela Zelbst|frame}}
'''Videos''' 
*'''Dr. Zelbst, Pamela. "Critical Path Method and PERT explained". (2015)'''This is a nice clip from youtube explaining the differences between CPM and PERT. First it explains in detail how the CPM can be used followed up by exampels. Secondly it compares the models. <ref name="DrP11">Dr. Zelbst, Pamela. "Critical Path Method and PERT explained" (2015)</ref>
{{#ev:youtube|watch|200|right|Critical Path Method and PERT explained by Andrew Bell|frame}}

*'''Bell, Andrew of coventry University. "Critical Chain Project Management". (2014)''' This video is about Critical Chain Project Management by Andrew Bell from Coventry University. the video also contains information about Agile Project Management. <ref name="Bell">Bell, Andrew. "Critical Chain Project Management" (2014)</ref>
{{#ev:youtube|www.youtube.com/watch?v=7Xf-waj23P8|200|right|Critical Chain Project Management by CEO Rob Newbold|frame}}

*'''Newbold, Rob. "Critical Chain Project Management". (2011)''' This Video is made by Rob Newbold who is CEO of ProChain Solutions. It gives an introduction to Critical Chain approach to project management and how it provides an opportunity to make improvements to how a compagny managers its projects. <ref name="Rob">CEO Newbold, Rob. "Critical Chain Project Management" (2011)</ref>

==Bibliography==
<references/>