The critical path method (CPM) was first used by Morgan R. Walker in 1957. It helps in ascertaining time schedules, makes better and detailed planning possible, encourages discipline and provides a standard method for communicating project plans schedules and to time and cost performance.

Critical path method (CPM) is a resource-utilization algorithm for scheduling a set of project activities. The essential technique for using CPM is to construct a model of the project that includes the following:

·         A list of all tasks required to complete the project

·         The dependencies between the tasks

·         The estimate of time (duration) that each activity will take to complete

With this information, you can determine the critical path by identifying the longest stretch of dependent activities and measuring them from start to finish.

Once you’ve identified which activities are on the longest, or critical path, you can more easily discern which have total float, or can be delayed without making the project longer.