Many thanks for the input Ronald. I did go back and chase up the dominant logic which was placing the constraints, giving the negative float. However, i am still bewildered as to why the negative float path occured, when I have been informed by primavera that the progress over-ride should not produce such calculations.
I can only, for the moment, conclude that the out of sequence activity, which had a SS +15 & FF +15 predecessor , was so tightly constrained but had an actual placed at such an out of sequence date, that the software could not appropriate a sensible calculation (after all in the real world, the change would have been noted, a new logic placed and then re-scheduled).
Many thanks for your thoughts once again.
Robert
Member for
22 years 10 months
Member for22 years10 months
Submitted by Ronald Winter on Wed, 2006-02-15 09:35
Off the top of my head, I would say that what you saw was the natural consequence of using the Continuous Activities CPM option and a mis-matched doubly-constrained activity. The logic constraining the start of the activity (perhaps Start-to-Start?) plus the activity’s duration did not match the logic constraining the finish of the activity (perhaps Finish-to-Finish?). One of the two constraints needed to be overridden and Primavera always chooses the finish constraint as the dominant one. This caused the activity to start 4 days later than logic says that it should (and hence, the -4 float value. This also assumes that you are using the Start Dates to Compute Float option.)
I forgot – P3e/c does not have an option to choose Continuous versus Interruptible activities for the CPM calculation. You always get Continuous. P3 has this option which will automatically stretch the activity duration to prevent this sort of thing.
Congratulations on your curiosity and diligence at actually reading the schedule and using your head. That is what makes for great Schedulers. Good luck!
Member for
22 years 1 monthRE: Creation of negative float, when end date’s is zero
Many thanks for the input Ronald. I did go back and chase up the dominant logic which was placing the constraints, giving the negative float. However, i am still bewildered as to why the negative float path occured, when I have been informed by primavera that the progress over-ride should not produce such calculations.
I can only, for the moment, conclude that the out of sequence activity, which had a SS +15 & FF +15 predecessor , was so tightly constrained but had an actual placed at such an out of sequence date, that the software could not appropriate a sensible calculation (after all in the real world, the change would have been noted, a new logic placed and then re-scheduled).
Many thanks for your thoughts once again.
Robert
Member for
22 years 10 monthsRE: Creation of negative float, when end date’s is zero
Off the top of my head, I would say that what you saw was the natural consequence of using the Continuous Activities CPM option and a mis-matched doubly-constrained activity. The logic constraining the start of the activity (perhaps Start-to-Start?) plus the activity’s duration did not match the logic constraining the finish of the activity (perhaps Finish-to-Finish?). One of the two constraints needed to be overridden and Primavera always chooses the finish constraint as the dominant one. This caused the activity to start 4 days later than logic says that it should (and hence, the -4 float value. This also assumes that you are using the Start Dates to Compute Float option.)
I forgot – P3e/c does not have an option to choose Continuous versus Interruptible activities for the CPM calculation. You always get Continuous. P3 has this option which will automatically stretch the activity duration to prevent this sort of thing.
Congratulations on your curiosity and diligence at actually reading the schedule and using your head. That is what makes for great Schedulers. Good luck!