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TEAMFLY80 CRITICAL PATH SCHEDULING

The forward pass establishes a pair of early dates for each task. These are
called Early Start and Early Finish. The backward pass establishes a pair of late
dates. These are called the Late Start and Late Finish. The difference between
the early dates and the late dates is the total float.

Tool Tip Sometimes the user does not wish to publish the late
dates or the float. This is controlled in the reporting process. In
such situations, it is also popular to change the name of the
early dates to something like Scheduled Start and Scheduled
Finish, or perhaps just Start and Finish. Just about all programs
allow the user to rename the standard calculated fields.

Also, at times, the user does not wish to calculate or publish
the early dates. Instead they want to have the dates calculated
and displayed as the latest dates. This would be equivalent to a
just-in-time scheduling approach. Most products have an ALAP
(as late as possible) calculation option that can be used to ac-
complish this. The default is the ASAP (as soon as possible) mode.

Date Constraints Now that we understand how the CPM calculates schedule
dates, we can understand how to use imposed dates and how they affect the
schedule calculations. Of the several options to impose dates, the most popular of
these is the Start No Earlier Than (SNET) or Finish No Later Than (FNLT).

The SNET dates are used to impose a task start date that may be later than the
earliest start as determined by the computer. They may override the forward pass
calculations. For example, the computer may determine that a ditch can be exca-
vated starting on January 15 (based on completion of identified predecessors). How-
ever, your crew may not want to initiate any excavation work (in Montana) prior to
March 15, due to the frigid weather. By imposing a SNET date of 3/15, the calcu-
lated early start of 1/15 is overridden. Note that if, for any reason, the predecessors
slip out beyond the 3/15 date, the imposed date is now overridden by the naturally
calculated date. This is why we call such an imposed date Start No Earlier Than,
rather than Start On, which is a forced date that is not overridden by the calculations.

Trap First time users of project management software often
tend to overuse imposed dates, especially the Start On option.
In an attempt to force the schedule to predetermined dates,
this improper use of the Start On option creates two problems.