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TEAMFLY90 CRITICAL PATH, CRITICAL CHAIN, UNCERTAINTY

constraints. Next, it identifies the critical chain. The next steps create and insert
the various buffers. Options are provided to set the parameters for the buffers
and to override the automatic placement or computation. A Factor Durations op-
tion can be used to set a duration multiplier. For instance, you might want to use
the Duration Factor to cut the task durations in half, and then set the buffer op-
tions to 50 percent of the path duration. In the brief test that I ran, I had to re-
duce the durations by about half to compensate for the added duration for all the
buffers. Also, in this test, the project duration (after load leveling, but without
buffers) was the same as when I invoked MSP’s resource leveling function (which
I would expect). However, the selected sequence of task execution was different.

If you don’t wish to use separate software for CCPM, some of the functions
can be achieved via creative use of traditional CPM software that has PERT
(three-time-estimate) capabilities. This is available in Scitor’s Project Scheduler
as well as in MS Project (version 98 and later). Neither of these products will cal-
culate and place buffers, but the PERT analysis can be used to estimate the time
that should be allocated for schedule contingency.

Tool Tip Scitor’s latest scheduling release, Project Scheduler
8, is the first traditional CPM program to offer support for
CCPM as an available option within the basic product. PS8 of-
fers a complete Critical Chain capability as a scheduling option
within the basic program. The CCPM capability in PS8 has sup-
port for multiproject critical chain scheduling, based on proj-
ect priorities and constrained by key resources (Drum
Resources feature). Scitor can be reached at (408) 745-8300, or
at www.scitor.com.

Planning and Tracking Issues

It must be obvious by now that the road to good schedules is strewn with rocks
and other impediments. Our plans must contain a balance of reasonable task du-
rations and reasonable contingency. We must squeeze the fat (or excessive contin-
gency) out of the estimates, yet retain a reasonable cushion for the inevitable
effects of Murphy’s Law. There are several techniques for dealing with these
scheduling issues, including PERT estimates (triple time estimates) and Critical
Chain buffers.

But once these plans are drafted, we cannot rely on just a single method of
tracking progress. Those of us who were taught to manage via the critical path