Schedule Development
Network logic and float
Schedule development turns planned activities into a logic network and calculates dates through the critical path method. Use finish-to-start, start-to-start, finish-to-finish, and start-to-finish ties with intention; lags and leads should be justified, not used to hide missing logic. Calendars affect when work can occur and therefore change dates and float. Constraints such as start-no-earlier-than or finish-no-later-than can create negative float and must be documented.
Critical path traps
The critical path is the longest path through the network and normally has the least total float. Multiple critical paths can exist, and a path with zero float is not automatically the longest if constraints or lags distort the network. Do not confuse total float with free float. Total float = LS − ES = LF − EF; free float = earliest successor start − EF. Open ends-activities without predecessors or successors-can make float results meaningless.
Worked example
An activity has ES 10, EF 16, LS 13, and LF 19. Total float = 13 − 10 = 19 − 16 = 3 days. If its only successor starts at 17, free float = 17 − 16 = 1 day. The activity can slip 3 days without delaying the project, but only 1 day without delaying that successor.
Development outputs
Baseline the reviewed network only after checking logic, calendars, constraints, float, and resource assumptions. A schedule that calculates is not the same as a schedule that is valid.