Float Negative

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Anderson Charlie
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Hi,

I'm doing tracking of activities % for my project. I keep getting the total float for the activity which i updated negative eventhough the % is not zero and it started ahead of the scheduled date. Could anyone help me? Been cracking my head on this. Appreciate if someone could assist. 

 

Thanks.

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Rafael Davila
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I hope you are not using P6 as it is notorious for how unreliable its float calculations are. If using P6 take a look at the following link that can provide you a clue on additional places to look.

https://www.linkedin.com/pulse/story-behind-negative-float-p6-assem-sher...

Rafael Davila
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Check the following issue that at times is overlooked.

The Must Finish By date can be thought of as a project level constraint. Once the last activity in the schedule exceeds this date, negative float will appear.

https://tensix.com/2012/01/oracle-primavera-p6-must-finish-by-date-2/

Be careful when interpreting negative float as P6 replaces late dates instead of using CPM original algorithm.

Good scheduling software do not enforce the impossible, late dates being earlier than early dates, unfortunately this is how most current scheduling software works. In such case a better mathematical approach is to set late dates equal to CPM original algorithm early dates, but never late before early as Spider Project do. This will show true current criticality. If you still want to see negative float it shall be done using a separate field for negative float dates. Real constraints such as contractual date constraints shall be modeled, but with appropriate mathematical concepts.

With appropriate algorithms there is room for both calculations, otherwise you will be better off if following Mike's advise and better keep independent milestones to flag the overruns.

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Good Luck

Kannan CP
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Hi Anderson,

As you specified, the actual start of the activity ahead on 12th June. Check what is the planned completion and the updated programme forecast completion. You need to check the longest path in the programme-i hope you are using P6.

If an activity got delayed it doesn't mean that it will affect the project completion, unless it is in the critical path or it has no more float.

If your progress is higher than plan but your project in delay, it means that non critical activities(which are now ahead) could be showing that progress and the real critical activities pushing the compleion date without any progress. You need to concentrate on the real critical path or the longest path.

I hope this help.

BR

Kannan

Anderson Charlie
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Hi Kannan,

In some cases for my tracking, some of the activities the scheduled completion date is still far ahead. I.e the activity planned to start on 1st July but the actual start date was 12th June same year. The scheduled completion is let say next year. For your information, my work program is retained logic base and not using the Earned Value Method. Which I understand, any lower rate produce that scheduled rate on that month of tracking P6 will identify that activity as potential delay. Am I correct? 

Hope can assist me in this. I don't how to answer to my management for every progress meeting. My actual %age progress is higher than scheduled %age progress but still my project having a delay.

Thanks.

Kannan CP
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Anderson,

The activity may have started earlier than plan, but the progress could be too low so that the planned completion date is slipped. This may be creating the negative float.

 

BR

Kannan

Mike Testro
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Hi Charlie

Where the task is inthe programme is irrelevant.

Just take the constraint off and the negative float will disappear.

You will also discover the true completion date of your project.

Best regards

Mike T.

Anderson Charlie
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Hi Mike,

I understand that when an activity exceed it Must Finish On constraint date, the float will be negative. But in my case, my activity does not have any constraint. It starts earlier than the scheduled date eg. scheduled date is 1st July 2016 but activity started in 12th June 2016. 

Patrick Weaver
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Mike is 100% correct Charlie, for more on the issue see: http://www.mosaicprojects.com.au/PDF/Schedule_Float.pdf (page 4)

Mike Testro
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Hi Charlie

Negative float only happens if there is a constraint in the down stream logic.

Calendar settings can also cause it.

So track the downstream logic to find the blockage.

Best regards

Mike T.