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Hi all,
I am looking to resolve some negative float on a P6 schedule handed over to me.
Please note:
1. There are no hard Constraints
2. No 'Must Finish By' on the project date
3. No external relationships
As you can see below, the on the 'Project Start' activity the 'Late Finish' is earlier than the 'Early Start'. (DD is July-22).
Any help would be appreciated!
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Does this schedule have instances in which a Finish Milestone has a different calendar than its predecessor activity? For example, a 7 day/week activity ends on a Saturday, and then the following work is on a 5 day/week calendar. I have found by times that this can lead to negative Total Float. In those cases, I have found an acceptable work-around is to insert a short "buffer" activity between the aforementioned activities, setting it to the 5 day/week calendar; it needs to be only long enough to absorb the negative Total Float.
Does this schedule have instances in which a Finish Milestone has a different calendar than its predecessor activity? For example, a 7 day/week activity ends on a Saturday, and then the following work is on a 5 day/week calendar. I have found by times that this can lead to negative Total Float. In those cases, I have found an acceptable work-around is to insert a short "buffer" activity between the aforementioned activities, setting it to the 5 day/week calendar; it needs to be only long enough to absorb the negative Total Float.
Does this schedule have instances in which a Finish Milestone has a different calendar than its predecessor activity? For example, a 7 day/week activity ends on a Saturday, and then the following work is on a 5 day/week calendar. I have found by times that this can lead to negative Total Float. In those cases, I have found an acceptable work-around is to insert a short "buffer" activity between the aforementioned activities, setting it to the 5 day/week calendar; it needs to be only long enough to absorb the negative Total Float.
Does this schedule have instances in which a Finish Milestone has a different calendar than its predecessor activity? For example, a 7 day/week activity ends on a Saturday, and then the following work is on a 5 day/week calendar. I have found by times that this can lead to negative Total Float. In those cases, I have found an acceptable work-around is to insert a short "buffer" activity between the aforementioned activities, setting it to the 5 day/week calendar; it needs to be only long enough to absorb the negative Total Float.
thats impossible if what you say is true then the backward pass late finish will equal the forward pass early finish and the float will ALWAYS be zero
There are a couple more methods that create Negative Float missed out from the responses above and Gert Truyen's document:
1. If you import a file from another database and the original project has External Relatonships then the imported file will have External Early Starts and External Early Finish Constraints representing the missing relationships which can cause Negative float. The Start and/or Finish dates will have an "*" and the constraints may be removed from the Extenal Early Start and External Early Finish columns.
2. Also if you do not use Retained Lag and have a Loop in the logic and an activity with Actual Finish then the software will not give a looping logic error and create negative lag, see my article here: http://eastwoodharris.com/DL/TP/190416_Understanding_P6_Schedule_Options_When_scheduling_activities_use.pdf
There are a couple more methods that create Negative Float missed out from the responses above and Gert Truyen's document:
1. If you import a file from another database and the original project has External Relatonships then the imported file will have External Early Starts and External Early Finish Constraints representing the missing relationships which can cause Negative float. The Start and/or Finish dates will have an "*" and the constraints may be removed from the Extenal Early Start and External Early Finish columns.
2. Also if you do not use Retained Lag and have a Loop in the logic and an activity with Actual Finish then the software will not give a looping logic error and create negative lag, see my article here: http://eastwoodharris.com/DL/TP/190416_Understanding_P6_Schedule_Options_When_scheduling_activities_use.pdf
There are a couple more methods that create Negative Float missed out from the responses above and Gert Truyen's document:
1. If you import a file from another database and the original project has External Relatonships then the imported file will have External Early Starts and External Early Finish Constraints representing the missing relationships which can cause Negative float. The Start and/or Finish dates will have an "*" and the constraints may be removed from the Extenal Early Start and External Early Finish columns.
2. Also if you do not use Retained Lag and have a Loop in the logic and an activity with Actual Finish then the software will not give a looping logic error and create negative lag, see my article here: http://eastwoodharris.com/DL/TP/190416_Understanding_P6_Schedule_Options_When_scheduling_activities_use.pdf
There are a couple more methods that create Negative Float missed out from the responses above and Gert Truyen's document:
1. If you import a file from another database and the original project has External Relatonships then the imported file will have External Early Starts and External Early Finish Constraints representing the missing relationships which can cause Negative float. The Start and/or Finish dates will have an "*" and the constraints may be removed from the Extenal Early Start and External Early Finish columns.
2. Also if you do not use Retained Lag and have a Loop in the logic and an activity with Actual Finish then the software will not give a looping logic error and create negative lag, see my article here: http://eastwoodharris.com/DL/TP/190416_Understanding_P6_Schedule_Options_When_scheduling_activities_use.pdf
The first thing you look for when you see a negative float is the constraints that are applied to the schedule, but that is not the only reason that generates the negative float in P6. In the absence of date constraints P6 can inadvertently still cause negative float[1]. Somehow this flaw is still overlooked by many of the “experts” in scheduling as if it never happened.
P6 has a calculation option called, “Actual Dates.” If the Actual Dates option is selected, then the predecessor’s late finish is set to the time unit before the actual start of the out-of-sequence successor. This assignment has the potential of creating negative float without date constraint[2].
[1] 5 reasons why your P6 schedule contains negative total float
if items 1,2, and 3 are correct as you stated then the Late finish MUST equal the Early finish and total float will ALWAYS be zero
this is the basis for CPM calculations this is how the algorithm works
Email: PPadmin@planningplanet.com
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