Page 70 -

FIGURE 4-3. Example of a project schedule showing a critical path
This helps the project manager make decisions about the project. For example, if an extra
person becomes available for the project, the project manager can assign him to tasks on
the critical path, since assigning him as a resource on a noncritical task won’t have any
noticeable effect on the due date. It also helps the project manager understand the impact
of scope creep or changing requirements, by showing whether those changes will make a
difference in the time to deliver.

Don’t Abuse Buffers
Many project managers commonly add buffers to their schedules. A buffer is a task added
to the schedule with no specific purpose except to account for unexpected delays. This

practice involves either adding extra tasks or padding existing tasks at strategic points in
the schedule where overruns are “expected.”
There are times when buffers are useful. For example, on a year-long project, if every pro-
grammer has two weeks of vacation and on average takes one week of sick days, then the
project is guaranteed to lose three person-weeks of effort over the course of the year. The
project manager could sprinkle three person-weeks of buffers at strategic points in the
schedule in order to accommodate for this known loss. The use of buffers in this case is
appropriate because the size of the loss is known.

However, there are many times when buffers are abused. The idea that overruns are
expected means that there is an implicit assumption that the estimate is incorrect. If this is the
case, why not increase the estimate to include the buffer? The danger in the buffer is that it
lulls people—especially senior managers under time pressure—into feeling that there is lots
62 CHAPTER FOUR