Total Slack Column Recalculation

[JimS]

I understand Total Slack, and I like to use it to identify "close" deadlines.
Recently, I was running a scheduling session, opened up a column to display
"Total Slack", and began making changes to critical tasks to alleviate their
tightness. The schedule has no resources assigned, very few constraints (I
hate them), and a fair number of subprojects heirarchically defined with
deadlines on each task. The project end date does not constrain.

When I changed the deadline on a critical task, or changed the duration, I
expected the Total Slack column to recalculate appropriately. For example, I
might move the deadline out on the sequence of tasks so as to relieve the
pressure on that sequence ("We don't need that as soon as we expected....")
What I found was that the Total Slack column did not update. It stayed the
same, no matter what we did with respect to durations or deadlines.

I expected it to adjust in real time. Why didn't it?

 

[Jan De Messemaeker]

Hi,

Either you did not relieve the tasks from their deadlines (a deadline on
each task, why???)
or Calculation was set to Manual in Tools, Options, Calculation.
Total Slack is by far the most useful when there are very few deadlines and
the project's dates are conditioned by the relationships.
You hate constraints? As for slack calculations, deadlines work identically
as Finish no later than...
HTH

 

[JimS]

I don't have to have the deadline on each task, just the last one. You are
correct. It just turns out to be convenient on the presentiation to have a
"line" of deadlines. They're all the same date within a given sequence, so
they have no affect on the earlier tasks in the sequence.

I don't have a single, long project, but a series of scores of small
projects that last a couple of months each, each with its own exogenous
deadline. Using a deadline instead of a FNLT constraint allows me to
conveniently display the deadline, and allows tasks to flow past the deadline
so we can see how broken they are.

Long-winded response. I'm sorry. Anyway, my calculation is set to automatic.
I'll do some further work to see if something is constraining the sequence I
have missed. I have the bars turn red when they're critical. When I change
the deadline, the bars change back to blue, and the red warning diamond goes
away, but the Total Slack column stays where it was.
I set the deadline dates using VBA by querying an outside database about
equipment deliveries. My project sequences are in preparation for equipment
deliveries, so if the equipment delivery changes, so might my target date.