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CPM and Milestones
In a project using the critical path method (CPM), most tasks are outlined, defined and scheduled; some of them are critical and some are not. Using CPM helps managers to determine how long a project will last in duration and how many resources a project will need it order for it to be completed.
In CPM, task--the activities that must be performed--are deemed critical or non-critical. They can be assigned and worked on independently of one another. PERT charts are often used in CPM to define milestones or events.
Unlike tasks, which are activities that teams or individuals perform, milestones are events that mark activities completed prior to revealing the milestone or event.
Milestones are then marked on PERT charts or network diagrams in tens; i.e., milestone 10, milestone 20. The reason for the large gap in marking milestones offers the project manager the option to add tasks if it becomes clear they are needed in order to complete the project.
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The Importance of Milestones
Critical path milestones are essential when using CPM. Unlike other project management methodologies, CPM, which is not as popular as it was in the 1950s, can identify variables, causes, and effects within a project or process.
We can take a look at why the DuPont Corporation developed CPM in the first place back in the 1950s: It was used to analyze what would happen if the company closed down manufacturing plants for maintenance and then reopened them once maintenance was complete.
DuPont could identify through CPM the following:
- Required Maintenance
- Amount of Shut-Down Time Needed
In this example, once the required maintenance is determined and the amount of time needed to shut down, tasks can be assigned based on the project itself. Milestones in CPM are a compilation of tasks that are successfully completed. On the other hand, if a risk is not identified properly upfront, such as the time needed to replace all lighting in the factory, a milestone must be inserted into the PERT chart, perhaps milestone 15 between milestones 10 and 20. Learn here on Bright Hub PM how to create a PERT chart in Microsoft Excel.
Think of CPM as an analytical way of completing a project and the importance of identifying all tasks in order to achieve certain milestones before the project can proceed.
In our factory example, if replacing the lighting wasn’t included or identified as a milestone, upon completion of the project, the factory maintenance would not be correct or successful. Therefore, the importance of allowing room for additional milestones, both critical and non-critical through the creation and analysis of the PERT chart in CPM can ensure that through this analytical process, projects can be successful.
In today’s world of project management, Six Sigma and Agile Management are ways that also identify not just milestones, but in what succession or order processes or procedures must be completed in order to finish a project.
Although CPM is not as popular as some of the project management trends that have come into use, it has been effective, especially if utilized in conjunction with PERT charts and establishing clear critical path milestones with enough room for change if critical issues are identified throughout the project and still allow enough scheduled time for project completion.
Image Credit: 5N PERT Graph with Critical Path 2 (IIIes) under the public domain at Wikimedia Commons