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Some tasks have slack naturally because they occur during the life of a longer
task with which they share a dependency. The shorter task could actually be
delayed until the end of the longer task without delaying the project.
Think about this example: You can start installing the plumbing and electrical
elements of a new office building as soon as the framing inspection is
complete. The plumbing takes two weeks, and the electrical work takes one week.
The next task, mechanical inspection, can’t happen until both the plumbing
and electrical tasks are finished. The shorter of the two (electrical) has a
week of slack because nothing else can happen until the dependent task,
plumbing, is finished (as in Figure 10-12). However, if electrical runs one week
late, the electrical task becomes critical.
These natural cases of slack occur in any project. In many cases, though, you
have to build in slack. Slack can be added in a few ways.
First, you can simply inflate task durations. Add two days to the duration of
all the tasks in your project, or go in and examine each task to figure out the
risk of delay and pad each duration accordingly. This method is a little
problematic, however, because when changes occur, you may have to go into
many tasks and adjust durations to deal with a schedule that’s ahead or
behind. You also have to keep track of exactly how much slack you built into