Calculating the
Critical Path
Calculating the critical path is the most quantitatively
intensive schedule management task to be done, perhaps more complicated than
"resource leveling" and the calculation of merge points. Though intensive,
critical path calculations are not hard to do, but on a practical basis critical
path calculations are best left to schedule network software tools. The
calculation steps are as follows:
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For each path in the network that connects all the way
through, and in our examples we will employ only networks that do have paths
that connect through, calculate the
so-called "forward path" by calculating the path length using the earliest start
dates.
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Then for each path in the network, work in the opposite
direction, using latest finish dates, and calculate the "backward path."
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One or more paths calculated this way would have equal
lengths, forward and backward. These are the critical paths. All other paths
will have unequal forward and backward lengths. These paths are not
critical.
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The amount of forward-backward inequality in any path is the
float or slack in the path. Overall, this path, or any one task on this path,
can slip by the amount of the forward-backward inequality and not be more than
critical and therefore not delay the project.
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