I wonder if you are using the term "critical path" correctly. No offense
intended if I'm mistaken but it is a very common error. "Critical" in this
context has nothing to do with "important" or "priority" and you spoke of
"prioritize accordingly." A "Critical task" is one whose delay will result
in a delay in the completion of the project. That's all it means. As such,
even a very low priority, trivial task can be a critical task. If a task
has any slack at all, it is not critical since it could be delayed by as
much as its slack time before the project finish gets delayed. A task that
is critical can have non-critical predecessors and vice versa, depending on
what else is going on in the plan and what contraints may be on it.
Likewise, just because a task had slack time doesn't mean that a successor
task will also have slack and you can easily come up with plans that have
multiple chains through them where a task with slack has a predecessor that
doesn't. Consider, Task A with a duration of 5 days, task B with a duration
of 10 days, both of which are predecessors to Task C. Taski C is a
predecessor to D, the last task in the project. Now task A has 5 days slack
and is non-critical, task B has 0 slack and is critical as are C and D. But
now put a SNE constraint on C that is 5 days after B ends. NOW, both A and
B will be non-critical, and the critical path will pick up on C as the
earliest critical task. Why? A could be delayed 10 days before C is pushed
back and B could be delayed 5 days before the same thing happens so nothing
earlier than C is critical.
Constraints - any constraints at all other than SASAP, can really screw up
identification of the real critical paths. IMHO, constraints should only be
put on task if external events beyond negotiation or human control put a gun
to your head over it. You can't control when the ice melts to let your ship
out of the harbour - that's a "start no earlier than constraint" on moving
the shipment of parts. Your boss tells you it has to finish by X date or
you're fired? That's not a constraint, that's a deadline. You want it to
start on 15th June and enter it as a Start No Earlier Than constraint?
That's not a legitimate SNET constraint either, that's trying to kludge the
software into telling you what you want to hear will happen instead of
giving you a reality check by predicting what's really GOING to happen when
you try to work the project or at least what would happen in the most
efficient plan.
Hope this helps
--
Steve House [MVP]
MS Project Trainer/Consultant
Visit
http://www.mvps.org/project/faqs.htm for the FAQs
James Keenan said:
All - thanks for your help.
I need three critical paths as I am delivering a product into three
different areas (in effect three projects, with the same resources) and must
prioritise accordingly. I have removed the 1% complete items and replaced
them with 'Start no earlier' constraints.
My problem however remains - I have a task that has no predecessor, is on
track, has a 'Start no earlier' constraint, and 5 days total slack. The
successor is on the critical path - but as it has slack, I don't understand
how this is on the critical path?
