The Critical Path Method (CPM) - Construction Project Scheduling and Control - page 58

BEGINNING-OF-DAY OR END-OF-DAY CONVENTION
In this topic, for mathematical computations and for the sake of simplicity, we follow
the end-of-day convention: any date mentioned for an activity means the end of that
day. In this convention, projects usually start at the beginning of day 1, which becomes
the end of day 0. Almost all authors use this convention. Computer software pro-
grams, however, are more sophisticated: the start date follows the beginning-of-day
convention , and the finish date follows the end-of-day convention. These conventions
are explained further in the following examples.

THE CPM EXPLAINED THROUGH EXAMPLES
Example 4.1: Logic Networks and the CPM

Example 4.1

Draw the logic network and perform the CPM calculations for the schedule
shown next.

IPA a Duration b

Activity

A - 5

B A 8

C A 6

D B 9

E B, C 6

F C 3

G D,E,F 1

a Immediately preceding activity.
b In days.

Solution: The Forward Pass

The project starts with activity A, which starts at the beginning of day 1 (end of
day 0). It takes 5 days to finish activity A; it finishes on day 5 (end of the day).
At this point, activities B and C can start. Activity B takes 8 days; it can start
on day 5 (directly after activity A finishes), so it can finish as early as day 13.
Similarly, activity C can finish on day 11 (5 + 6). Activity D follows activity B.
It can start on day 13 (end of B) and end on day 22. Activity E must wait until
both activities B and C are finished. Activity C finishes on day 11, but activity B
does not finish until day 13. Thus, activity E cannot start until day 13. With
6 days' duration, activity E can then finish on day 19. Activity F depends on
activity C only. Thus, it can start on day 11 and finish on day 14. The last
activity, G, cannot start until activities D, E, and F are finished. Through simple
observation, we can see that activity G cannot start until day 22 (when the