Am I missing a contraint?

Peter,

I do not use P6 but always follow what is happening there as always something is learned.

About Expected Finish Constraint I used such within SureTrak, is not really a constraint but a remaining duration calculator that as the activity moves with time the remaining duration is changed as to fit Expected Finish Date. I found this functionality very useful to keep automatically updated long lead deliveries. Believe others use it as a duration calculator to determine required duration of an activity in order to finish on a specified date, not a bad idea as long as you make appropriate resource adjustments. I suspect if P6 has such functionality it shall be similar to SureTrak implementation, though not necessarily, this you have to find out.

By listening to what Mr. Ron Winter says in his site I have learned a lot, yes he is Primavera oriented but his observations have application within other software. Not until recently, by reading one of his articles I realized how important is to resolve out-of-sequence events, even those already finished. I was always an advocate of the prescribed good practice to take care of out-of-sequence issues as I believe you do not model the impossible, out-of-sequence modeling is modeling the impossible, same as when your software allows for negative float.

Most schedulers avoid negative float but unfortunately some of our specs even call for it, the implementation of Finish No Earlier Than constraint is not equal in all software, some do not recognize the impossible and do not model impossible dates that create negative float that in addition make late date S curves wrong.

Best regards,

Rafael

from:

http://forums.oracle.com/forums/thread.jspa?threadID=881584&tstart=0

There are two primary causes of negative float on activities.

1. If a Must Finish By constraint is assigned at the project level, this could cause negative float if the project cannot be completed by the constraint date. Check the Must Finish By date in Projects View, Dates tab. Clear the entry if you do not want  to constraint project finish date.

2. If a mandatory constraint is assigned to an activity, this could cause negative float if the predecessor activities do not have enough time to finish. Run a schedule report to check for constraints.

Other possible sources of negative float: Out of sequence progress. Correct the logic in the schedule or schedule using Progress Override or Actual Dates.

To learn about Late Dates on completed activities take a look at the following link, Article 3.1

http://www.ronwinterconsulting.com/Understanding_P6_Dates.pdf

Have you checked a Must Finish Constraint for the overall project? A constait type that is not applied at the activity level but at the job level.

Late Finish constraints shall not be enforced when Late Dates become earlier than Early Dates, is a wrong application of a mathematical computation, modeling the impossible is wrong. That it is a mathematical computation is no excuse to use it wrong. In occasions it will allow for your early and late curves cross each other, obviously wrong, but even when this does not happens the late date curves will still be wrong under the presence of negative float, no excuses to use a wrong concept. Under resource leveling this gets even worse.

Even if you are in need to see contractual late dates you still need the constraints to be applied correctly. Look for software with the correct math.

By the same token, if your Resource leveling allows for over-allocations you are modeling the impossible.

Best Regards,

Rafael

BEHEAD NEGATIVE FLOAT

BEHEAD OVER-ALOCATIONS OF RESOURCES

modeling the impossible is wrong

Hi Peter

Just take off all constraints and reschedule to see what happens.

Also check your calendars.

Best regards

Mike Testro