The PERT chart was developed by the US Navy to show a project's dependencies. PERT stands for Program Evaluation Review Technique. In the PMI, PERT is also a formula (tool) used to estimate likely project duration according to the theory D = (P + 4M + O) / 6 where D = Duration, P = Pessimistic duration, M = Median/Modest duration and O = Optimistic duration.)