time-lags

The Critical Path Method (CPM) is a project scheduling technique to analyze and represent the tasks involved in completing a given project. It incorporates a trade-off between an activity’s duration and cost and relies on concepts similar to the program evaluation and review technique (PERT, see “The Program Evaluation and Review Technique (PERT): Incorporating activity time variability in a project schedule”).

The Program Evaluation and Review Technique (PERT) is a project scheduling technique to analyze and represent the tasks involved in completing a given project. It incorporates activity duration variability and relies on similar concepts as the critical path method (CPM, see “The Critical Path Method (CPM): Incorporating activity time/cost trade-offs in a project schedule”).

The critical path is a series of project activities with a zero slack value connected by precedence relations (see “Scheduling projects: How to determine the critical path using activity slack calculations?”). It contains all activities that are critical for the project duration and results in the generally accepted critical path rule:

A project network consists of a set of activities, represented as nodes in a network between which links are drawn to represent the technological precedence relations between these project activities (see “Activity links: How to add precedence relations between activities?”). 

These precedence relations can be one out of four types (start-start (SS), start-finish (SF), finish-start (FS) and finish-finish (FF)), with a positive, zero or negative time-lag to express a minimal or a maximal time window between two activities.