Critical path method (CPM) is a schedule network analysis technique. It determines the amount of float, or schedule flexibility, for each of the network paths by calculating the earliest start date, earliest finish date, latest start date, and latest finish date for each activity. This is a schedule network analysis technique that relics on sequential networks (one activity* occurs before the next, or a scries of activities occurring concurrently arc completed before the next scries of activities, and so on) and on a single duration estimate for each activity. Keep in mind that CPM is a method to determine schedule durations without regard to resource availability.
The critical path (CP) is generally the longest full path on the project. Any project activity with a float time that equals zero is considered a critical path task. The critical path can end under a few conditions. When activities with float time use up all their float, they can become critical path tasks. Or you may have a milestone midway through the project with a hnish-no-latcr-than constraint that can change the critical path if it isn't met.
Float time is also called slack time, and you'll sec these terms used interchangeably. There arc two types of float: total float and free float. Total float (TF) is the amount of time you can delay the earliest start of a task without delaying the ending of the project. Free float (FF) is the amount of time you can delay the start of a task without delaying the early start of a successor task.
In the following section, you'll calculate the CP for a sample project and illustrate how all the dates, the CP, and the float times arc derived.