Page 177 - DCAP601_SIMULATION_AND_MODELING

Unit 10: Simulation of a PERT Network (II)

Notes
Figure 10.2: Calculating the Early Start and Finish

3. Preliminary with the tasks at the end of the diagram, calculate the late start and late finish
for each task in turn, following the arrows in the reverse direction to the previous task, as
in the diagram below. The late finish is the same as the late start of the following task (for
the final tasks in the project, this is equal to the earliest completion date). If there is more
than one successor task, then there are several possible late figures. Select the smallest of
these. The late start for each task is the late finish minus the duration of the task. The final
calculation is for the earliest completion time for the project. This is calculated in the same
way as the early start date.
Figure 10.3: Calculating the Late Start and Finish

4. You now have, for each task, the initial and latest times that it can start and finish. Now
find the slack time (or ‘float’) for each task by subtracting the early start from the late start.

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