What do construction crews, software developers, and NASA have in common? They, and many others, use CPM scheduling to manage projects and predict the amount of time a project might take. CPM, or critical path management, is essentially a project management technique that identifies milestones and activities in any given project.
Basic CPM Scheduling Technique
Before understanding the basic technique, there a few terms that are important to know. First, what does critical path mean in the first place? A project’s critical path is the shortest possible project duration. That means it’s order of activities with the shortest durations that add up to the shortest total project time.
Float is another important term that refers to the amount of time that an activity in your project can take without delaying the project’s overall date of completion or the next activity’s start date.
To set up your own CPM schedule, you will need to know the following:
- A list of activates that need to be done for the project to be completed,
- An estimated amount of time each activity will take,
- Dependability between activities.
To determine the first two, depending on the size and scale of the project, you typically only need to work backward from the end result to determine what you’ll have to do and how long it will take. For instance, if you want to paint a room, you know you’ll need to:
- choose a paint
- buy the paint
- buy brushes and rollers
- remove furniture from the room
- paint the borders
- paint the walls
- clean the brushes
If you know generally how long each of those activities will take, you have the first two prerequisites complete. Determining dependability between the activities means looking at the list of tasks and finding ones that need other activities to be competed before they can begin. For example, you can’t paint the walls before you choose the paint.
Once you know the dependability between different activities you can determine an ideal order of activities. That, coupled with the amount of time each one will take, can help you find the total duration of the project and the starting time for each activity.
Critical Path Scheduling
Scheduling something like painting a room seems fairly straightforward but larger projects can be more complicated. In that case, you would need to determine an optimistic early dates and realistic late dates. With those dates, you can calculate each task’s total float with the following equation:
Total Float = late start – early start (or late finish – early finish)
Once you have the total float for each activity you will be able to see the critical path schedule by which activates have the lowest float or no float.
The critical path method helps you determine three things about your project: the dates that each activity should start and end, the date the overall project will end, and your project’s critical path. The best use for CPM scheduling is when a project involves activities with unknown durations. Great for situations which activity durations are unknown.