Recently, I have been training some folks on CPM. CPM stands for "Critical Path Method" (aka Critical Path Analysis).
It is a method for diagramming (beginning at "finish" and working backwards to "start") the project tasks and then assigning durations to each. Once this is complete you calculate the early Start/Early Finish and Late Start Late finish for each task. This gives you the Float (aka Slack) on each path and, consequently, the Critical Path to your project.
What is Critical Path? Well, it's the path with zero slack. One day slip on the critical path is a day slipped on the end of the project date. This slippage usually costs the project additional Time, Money and resources.
The inverse is true as well. To compress the duration of your project, you must shrink (or "Crash") the duration of the Critical Path. Crashing, also, usually costs the project more Money/Resources.
It is possible that the critical path will change over the duration of the project. Therefore, some deeper analysis of the Critical path is truly important to successful project management. There are methods for examining the money to be spent on managing critical path.
What does CPM have to do with MS Project?
Microsoft Project 2007 (and all earlier versions) use the CPM to schedule tasks. Or, said another way... (you are now about to truly understand this tool... ) Project bases all it's calculations on a rules based path. It calculates the path, based on any exceptions you define like resource availability, specified start or end dates, etc...
For more information on Project and CPM visit this article
http://office.microsoft.com/en-us/project/HP012260691033.aspx
-------------------------- More Info on CPM -------------------------
Wikipedia says:
"The Critical Path Method, abbreviated CPM, or critical path analysis, is a mathematically based algorithm for scheduling a set of project activities. It is a very important tool for effective project management.
It was developed in the 1950s in a joint venture between DuPont Corporation and Remington Rand Corporation for managing plant maintenance projects. Today, it is commonly used with all forms of projects, including construction, software development, research projects, product development, engineering, and plant maintenance, among others. Any project with interdependent activities can apply this method of scheduling.
The essential technique for using CPM is to construct a model of the project that includes the following:
- A list of all activities required to complete the project (also known as
Using these values, CPM calculates the starting and ending times for each activity, determines which activities are critical to the completion of a project (called the critical path), and reveals those activities with "float time" (are less critical). In project management, a critical path is the sequence of project network activities with the longest overall duration, determining the shortest time possible to complete the project. Any delay of an activity on the critical path directly impacts the planned project completion date (i.e. there is no float on the critical path). A project can have several, parallel near critical paths. An additional parallel path through the network with the total durations shorter than the critical path is called a sub-critical or non-critical path.
These results allow managers to prioritize activities for the effective management of project completion. Originally, the critical path method considered only logical dependencies between terminal elements. Since then, it has been expanded to allow for the inclusion of resources related to each activity. This capability allows for the exploration of a related concept called the critical chain, which determines the project duration from both time and resource dependencies.
Since project schedules change on a regular basis, CPM allows continuous monitoring of the schedule, allows the project manager to track the critical activities, and ensures that non-critical activities do not interfere with the critical ones. In addition, the method can easily incorporate the concepts of stochastic predictions, using the Program Evaluation and Review Technique (PERT) and event chain methodology.
Currently, there are several software solutions available in industry that use the CPM method of scheduling, see list of project management software. However, the method was developed and used (for decades) without the aid of computers (with pencil and paper).
There are drawbacks of this technique, as estimations are used to calculate times: if one mistake is made, the whole analysis could be flawed, causing major upset in the organisation of a project."
