Earliest Start Time (EST)
In Critical Path Analysis, the earliest possible time at which an activity can begin, based on when all preceding activi...
Formula
EST = Maximum of all preceding (EST + Duration) values
Real World
In planning the Crossrail project, engineers could not begin tunnel boring under the Thames until all preceding geological surveys and shaft-sinking activities reached their EST, setting the earliest possible tunnelling start.
Exam Focus
Where two or more paths converge at a node, always take the highest value from the forward pass — taking the lowest is the most common EST mistake.
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