Project Management

First, a word or two about graphical conventions used in the
diagram in Figure 7-12. Again, four dates are calculated for
each activity: early start, early finish, late start, and late finish.
In this example, these calculations are expressed in terms of the
number of days from project startup. On your project, they
would most likely be specific calendar dates.
On large projects, you can spot the critical path by examin-
ing the difference between the early dates and the late dates.
For example, in Figure 7-12, the difference between the early
start and late start of Activity C is six days. This means that
Activity C could start anytime within this window of time and
not impact the overall project schedule. However, notice the dif-
ference between the early start and late start of Activity E: zero.
This means that Activity E has no flexibility (float) with regard
to when it can start. Activity E is on the critical path.
The management implications of being aware of the critical
path are obvious. These are the activities that you’ll pay the
most attention to as you attempt to keep the project on sched-
ule, because one day of slippage in a critical path activity
means one day of slippage in the overall project.
One final note about critical path. Remember our discussion

132 Project Management

Activity A

0 8 8

0 100 8

Activity B

8 14 22

8 200 22

Activity C

14 8 22

8 300 16

Activity D

24 10 34

22 400 32

Activity E

22 12 34

22 500 34

Activity E

34 12 46

34 600 46

Activity Title

Duration

Activity #

Late Start Late Finish

Early Start Early Finish

Figure 7-12. Calculation of forward and backward pass