Critical path vs. Critical chain

Critical path is the sequence of tasks from beginning to completion of the project where total duration of sequenced tasks is higher than any other path. It is worked out by using activity on arrow diagram. Every activity in a diagram starts and ends at an event. For every event the needs Earliest Event Time and Latest Event Time needs to be calculated.

EET identifies the earliest date the activity can start but no sooner than the previous event is completed and LET identifies the latest start date without delaying the start of the next activity.

The longest path from the beginning to the end of the project with no room for slack is the critical path. Delay in any task’s completion in the critical path, delays overall project completion time.

Critical chain differs from critical path as it also takes into consideration resource availability as well as tasks precedence. If unlimited amount of resources are available at anytime then critical chain will be same as critical path. It is planned in same way as critical path and two durations entered for each task: best guess duration and safe duration. Then resources are assigned to each task. The longest sequence of resource-levelled tasks that lead from beginning to end of the project is the critical chain.