Displaying Total Slack at the Summary Level

[Rob]

Hi,

I'm using MSP 2000.

A project file I update each week has some subtasks with negative Total
Slack (the worst -59d) but at level 1 of the project, I get -6d. Also not
all of the summary tasks are reflecting the total slack values of their
children.

Assuming there are no flaws in the logic, my questions on what’s preventing
the correct float value from being rolled up are –

1) Is there a known bug in MSP 2000 or any MSP version?

2) Are there any limits on the WBS level for rolling up float?

3) Does over loaded resources have any influence on float?

4) Is there anyway to determine file corruption causing this problem?

5) What other signs would be present, if the logic was incorrect?

Any assistance in resolving this would be greatly appreciated.


Thanks

Rob

 

[DavidC]

Hi Rob,

One thing worth checking is the calendar assigned to the summary task, is
that different to the tasks with longer negative slack? If there is a
difference betwen the calendars, and the calendar for the summary task has
longer working time than the other tasks, then what you are seeing is correct
since the summary task could 'work' in some of the period where the task is
scheduled not to work. Since the slack is a simple mathmatical calculation
Project looks at the dtaes and does the calculation based on the calendar and
the default options for working time.

Hope this goes someway toward answering the question.

regards

DavidC

 

[davegb]

Hi,

I'm using MSP 2000.

A project file I update each week has some subtasks with negative Total
Slack (the worst -59d) but at level 1 of the project, I get -6d. Also not
all of the summary tasks are reflecting the total slack values of their
children.

I'm not sure what you mean here. How would a summary line "reflect" the
total slack values of the subtasks? If the CP runs through that
particular Summary line, the total slack would be zero, I think (don't
have Project here to check this out.) Otherwise, who knows what it
would be. Various subtasks would have differing amounts of TS, but the
summary line could have none or a lot. The TS of a Summary line is a
meaningless number, if you've linked correctly (no links to Summary
lines).

What relationship are you expecting?

 

[Rob]

David,
Thanks for your suggestion.
I've made sure all tasks (summary, subtasks & milestones) all have the
standard calendar assigned and it made no difference.
I've also copied portions of my live file into a new file and I still don't
understand why the Project summary task calculates -6d when its subtasks show
-59d.

I've set up small test files to examine the impact of constraints & status
on total slack values.
In one such file containing 8 tasks all F-S, I set a deadline far out into
the future creating plenty of +ve total slack(TS). I was amazed to see as I
indented a task, both the summary & child TS reduce, while the other tasks
still showed the original TS.
The summary / child task was calculating TS between the finish date of the
last child and the finish date of the last task (i.e. task 8). The TS would
continue to reduce until I indented task 7 giving TS = 0d while task 8 TS is
still its original+ve vlaue.
I donot believe this is the correct way MSP should be calculating TS.
What do you think?

 

[Rob]

Dave,

The relationship I'm expecting is - the Level 1 Project summary task to
summarise the information from its children. In this particular case (Total
Slack), I expect the lowest value being -59d to be displayed at the project
level not -6d.
Please read my response to DavidC with particular reference to the test file
example I talk about.
I look forward to further discussion on this.

 

[davegb]

Dave,

The relationship I'm expecting is - the Level 1 Project summary task to
summarise the information from its children. In this particular case (Total
Slack), I expect the lowest value being -59d to be displayed at the project
level not -6d.
Please read my response to DavidC with particular reference to the test file
example I talk about.
I look forward to further discussion on this.

I'm not sure what meaning this value would have. Since TS (for a task)
= LS - ES, which LS and which ES of all the subtasks would you use to
calculate the TS of the Summary line? The average? The median? The
earliest ES? Same thing with LS. In almost 30 years of studying and
teaching CPM, I've never seen or heard of Summary lines being included
in CPM analysis. This is one of the reasons why I strongly urge people
not to link to Summary lines, it detracts from the CPM analysis, makes
it meaningless.

To give meaning to this discussion, we first have to determine the ES
and LS of the Summary line. Can you give me cogent reasoning on how to
do that? Without it, wouldn't TS be indeterminant?

I agree that this is an interesting topic, I never thought of these
issues in this manner before.