Program evaluation & review technique (PERT) was first build in 1958 and 1959 to fulfill the needs of the era of increased engineering where the techniques of Gantt and Taylor was not applicable. Program evaluation & review technique was introduced by US navy in 1958 on its Polaris Weapon System. The Booz, Allen and Hamilton are the management consulting firm that assists in the development of this useful program evaluation & review technique. At that time PERT was rapidly becoming famous in almost all the industries but at the at same moment, DuPont Company started a new project of similar technique called Critical Path Method (CPM) which also becomes famous in mostly process and construction industries.