The Program Evaluation and Review Technique or PERT is a management tool developed in the 1950s by the U.S. Navy. It keeps projects on time by identifying the critical path.
For instance, let’s say it takes 10 days to lay the concrete and 5 days to put up the fence. Laying the concrete is the critical path. If the concrete workers are getting behind, you should divert workers from the fencing operation to work on the concrete and keep it on time. If the fence takes 7 days, the project will still finish on time, but if the concrete is late the project will not finish on time.