PERT and CPM are both methods for predicting the cost and completion time of projects ... and the time taken for each activity must be known or at least estimable. Some cases are too simple for PERT - ...

and cautions related to the PERT approach, refer to Moder, Phillips, and Davis (1983) and Elmaghraby (1977). A simple model is used here to illustrate how PROC CPM can incorporate some of these ideas.