MSP negative float and constriant

V
V Kutty 👤 Member for 15 years 6 months

Hi,

I was analysing a schedule for a contractor. The final milestone (constrained finish on or before) has a float of -78 days and a finish of 1 Jan 15. If I remove this constraint I was expecting the end date to move by 78 days to Middle of March. Instead the program moved by 152 days. Any idea why this may have happened?

Thanks,

Regards,

Vijay

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T
Tom Boyle 👤 Member for 19 years 7 months
· Permalink

Vijay,

(Presuming "MSP" in your title means Microsoft Project)

1. If the whole program moved to the right after removing a FNLT constraint, then the project is scheduled backwards, and you are in a heap of trouble.  Most people who use terms like "float" and "finish on or before" don't schedule like that.  (Check the Project Information dialog for  "Schedule from: = Project Finish Date" and note the Finish date.)  

2. If only the final milestone moved to the right after removing its FNLT constraint, then:

  • You have left the project schedule option for "Tasks will always honor their constraint dates" checked (this is the default setting.)  I would normally un-check it to prevent late constraints from overriding logic.  With the box un-checked, removing the FNLT constraint wouldn't "move" anything;  only the late dates and the float, not the scheduled (early) dates, would be affected.
  • Ignoring other constraints and funky logic, check the finish milestone calendar and the project's "hours per day" setting.  These have a great impact on the interpretations of durations and float.  For example, a milestone with a 24-hour calendar in a project with default settings (8hr/day) only needs to accelerate by one calendar day to recover 3 "days" of negative float. (This is not an issue in P6 because P6 calendars each include their own hours/day setting, while MSP only has one for the whole project.)
  • (Obviously) make sure there are no manually-scheduled tasks.

 Good luck, tom

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