Critical Path Method (CPM)

Earliest and Latest Event Times

• Earliest Event Time ($E$): the earliest possible time an event can occur, found by a forward pass through the network — for each event, $E$ is the largest of (the $E$ of every preceding event) plus (that activity's duration); at the very first event, $E=0$.
• Latest Event Time ($L$): the latest an event can occur without delaying the project, found by a backward pass, starting from the last event (where $L=E$ for the final event) and working backward — for each event, $L$ is the smallest of (the $L$ of every succeeding event) minus (that activity's duration).

Total Float of an Activity

$\text{Total Float} = (L_{\text{head event}} - E_{\text{tail event}}) - \text{Duration of the activity}$

Float measures the spare time an activity has — how much it could be delayed without delaying the project overall.

The Critical Path …