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THE MAGIC OF HAMMOCKS 113

Goldratt’s critical chain dissertations. However, practical application of some of
these concepts is possible using traditional CPM tools.

Tip When adding dummy tasks for contingency, be sure to
mark each of these with a code that can be used to identify
such tasks and to select such tasks for contingency monitoring
reports. By recording the baseline duration of these tasks (part
of the normal set baseline function), you can produce a vari-
ance report, noting all reductions of durations for contingency
tasks. You can even create an exception report, selecting only
contingency tasks that have reduced durations.

Regarding schedule contingency, there are three things that you can be cer-
tain of.

1. If there is no schedule contingency, the project end date will be missed.
2. If schedule contingency is not managed, the schedule will slip and the proj-

ect will be completed even later than if there were no contingency.
3. Murphy is working on your project.

A fuller discussion of the entire subject of project risks and contingencies is
presented in Section 6.

The Magic of Hammocks

We introduced the hammock function in Chapter 3.4. This capability, which,
incidentally, is not found in many CPM packages, has several handy uses. A
hammock is a type of task that does not have a fixed time duration. Instead, it
automatically calculates its duration from the tasks that it is associated with (or
group of tasks that the hammock spans). To illustrate, let’s go back to that ex-
pressway project. There are a number of tasks that are associated with the
erection of the new guardrails. We lay out and mark the location. We make
holes for the support posts. We place the posts. We attach and fasten the
guardrails. We may paint them. Finally, we complete the landscaping. All dur-
ing this period, we have to close the right lane and operate a flashing sign
warning of the lane closure.

How long do we need the sign and traffic cones? This is a piece of data that is
required to be entered when we add these activities. The answer is the duration is