CPM

Critical Path Method (CPM) is a formal, mathematical approach to scheduling and optimising project timelines, in 1957 revolutionising how industries managed complex projects.

DuPont needed a systematic way to plan plant maintenance and construction projects, where delays in key tasks could hold up the entire project.

CPM was designed to identify the longest sequence of dependent tasks (the critical path) that determines the project’s minimum completion time and to identify float, helping managers see which tasks can be delayed without affecting the final deadline.

CPM was developed by James E. Kelley Jr. of Remington Rand and Morgan R. Walker of DuPont and first used in 1957.

CPM

The process

• Activity Identification - The project is broken down into specific activities or tasks required to complete it. Each activity is identified and defined in terms of its duration, dependencies, and resources needed.
• Sequence of Activities - The sequence in which activities must be performed is determined. Dependencies between activities are established to create a network diagram that depicts the logical order of tasks.
• Estimation of Activity Durations - Each activity's duration is estimated based on historical data, expert judgment, or other estimation techniques. Optimistic, pessimistic, and most likely time estimates may be used to calculate a weighted average duration.
• Critical Path Determination - The critical path, which represents the longest path through the project network, is identified. Activities on the critical path have zero slack or float and, therefore, directly impact the project's overall duration.
• Calculation of Earliest Start and Finish Times - Using the forward pass technique, the earliest start and finish times for each activity are calculated based on its dependencies and duration. This determines the earliest possible project completion time.
• Calculation of Latest Start and Finish Times - Using the backward pass technique, the latest start and finish times for each activity are calculated based on project constraints and the critical path. This helps identify activities with slack or float.
• Identification of Slack or Float - Slack or float refers to the amount of time an activity can be delayed without delaying the project's overall completion time. Activities on the critical path have zero slack, while non-critical activities have positive slack.
• Resource Allocation and Leveling - Resources required for each activity are identified, and resource constraints are considered during scheduling. Resource leveling may be performed to resolve resource conflicts and optimize resource utilization.
• Monitoring and Control - Progress is monitored against the project schedule to ensure that activities are being completed as planned. Any deviations from the schedule are identified, and corrective actions are taken to keep the project on track.
• Continuous Improvement - Lessons learned from project execution are documented and used to improve future project planning and execution. This iterative process helps refine estimates, optimize scheduling, and enhance overall project management practices.

By following these fundamental principles, CPM enables project managers to effectively plan, schedule, and manage projects, optimize resource utilization, and deliver projects on time and within budget.

Critical Path Method and Chronograph

There is perhaps a notion that CPM is the precise way to plan a project and that therefore overruns are the fault of the people of the project, human factors. However it is a deeper problem then that in that there are some underlying assumptions in the CPM planning method that mean although it can work well in large production projects it may not work so well in small development project.

Large production projects tend to be project driven, people are hired as required to perform specific roles for known durations. A prime objective of the organisation is to complete the project in the minimum amount of time. The people are often contractors employed specifically to meet labour requirements. It is possible to hire any number of electricians, plumbers etc. They simply plug into the project because the project design drawings, methods etc. are all in standard language and also the roles are standardised.

Small development projects tend to be people driven, they are performed by a known and tested team of people each bringing particular capabilities to the project. A prime objective of the organisation is to keep that team effectively employed. The team might be working on multiple projects at any one time taking advantage of the synergies and interleaving work.

In small development projects, even if tasks and predecessor relationships are known, the project is very likely to depend on the special abilities of individuals in the organisation, one can't simply hire x people with the special ability to innovate.

Innovation is typically achieved by small teams of known people. Thus rather than a "project driven approach" we have a "people driven approach" where the availability of people typically controls the project. This has the potential to descends into a "scrum" as people throw more formal methods out the window.

However Chronograph supports agility within formal methods like Critical Path Method so there is every chance to retain a longer term schedule within the project.

A Talk about CPM

This is an advanced video on CPM but take a look at Mike Clayton's video courses which include some basic introductions. Mike's videos are no frills and contain a great deal of information gained through experience. We really like his work.

Project Management Briefing: Project Schedule

Antipatterns

Antipatterns? The patterns we get hooked on that are detrimental to our work.

What are Anti-Patterns?