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Slack Calculation in Summary Task - Project 2003

13 replies [Last post]
Mon, 2009-11-16 12:48
Bryan Eaton
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I am trying to show the minimum slack value for a summary task on my project. It seems only to show Maximum, which seems to be not very helpful in managing a project.

Is there a switch or option burried somewhere to set this to minimum?

At the moment I have set a Customized Duration field to equal the Finish Slack and set the rollup to minimum.

Thanks for all the help...
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Wed, 2013-11-20 18:41
#1
ahmed hamdy
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i made a schedule in ms project 2010 and the total slack equal zero,however there are many activities had big slack?

please advice

thanks 

ahmed

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Fri, 2009-11-20 16:25
#2
Rafael Davila
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The Start Slack field contains the duration between the Early Start and Late Start dates.

The Finish Slack field contains the duration between the Early Finish and Late Finish dates.

Total slack is calculated as the smaller value of the Late Finish minus the Early Finish field, and the Late Start minus the Early Start field. Total Slack is therefore the minimum of finish slack and start slack.

These after progress or activity splitting might differ.
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Fri, 2009-11-20 13:56
#3
Bryan Eaton
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Also looking at my detailed schedule, it dosnt make any difference at the subtask level - the total and finish slacks are the same, it only makes a difference at the summary level. Finish slack dosnt seem very helpful, total slack is helpful in combination with the minimum total or finish slack to help identify problem areas that might otherwise be missed. and yes you can always sort / group by your slack value to identify them too.

regards

Bryan
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Fri, 2009-11-20 13:47
#4
Rafael Davila
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10-4
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Fri, 2009-11-20 13:43
#5
Bryan Eaton
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And I get the same from 2003 - guess I was looking at finish slack rather than total slack - new terms to me. Its good to know what your looking at when explaining to management. Thanks for the Help...

Photobucket

Bryan
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Fri, 2009-11-20 11:10
#6
Rafael Davila
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This is what I got from MS Project 2007

roll up 2

As a reminder, slack is measured on the activity calendar.

Best regards,
Rafael
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Fri, 2009-11-20 09:09
#7
Bryan Eaton
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It seems the summary slack is calculated from the difference between the latest early finish and latest late finish of all the subordinate tasks.

So when I have an unlinked task in my group, it throws the calculation for a loop - speaks to the importance of having a properly constructed schedule with only activities that may impact the schedule. Irrespective of wether I think this is right or some other calculation would be appropriate, it is what it is. It is very important to know how it works so you can read the schedule correctly and explain it to managers. The help file needs to include the little snippet about how the summary slack is calculated.

Thanks for all your input.
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Wed, 2009-11-18 15:43
#8
Bryan Eaton
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The link talks about it being post SP1, I have SP2 loaded. My assumption is that this kb is already in SP2?

Regrgarding 2007, that software is only 2 years old, so does not qualify for use at my company, we recently upgraded from DOS!!! but seriously, I dont have it to try it out on...

Maybe you could try for me? It only needs a look at the summary float verses the subordinate tasks...
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Wed, 2009-11-18 11:18
#9
Rafael Davila
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Bryan,

Do you have the latests updates and fixes for MS Project 2003? Maybe you are doing the correct thing but the software does not show it. Perhaps you can try your file on MS Project 2007 to see if there is a difference.

Look at the following, might be a fix related to your issue.

http://support.microsoft.com/kb/891203

Best regards,
Rafael
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Tue, 2009-11-17 18:19
#10
Trevor Rabey
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Bryan, I am still scratching my head about this (the rollup on TF) but I can say something now.
You would be much better off sticking to consistent units for Duration, Days. It gets unnecessarily difficult to compare durations when you have days and weeks.
It is not really necessary to use the Duration1 field if all it does is repeat the Finish Slack and roll up. You could just Sort or Group or Filter by Finish Slack (Project, Sort/Group By/Filter).
The FF and SS links aren’t helping.

From MSP HELP:

Finish Slack (task field)
Data Type Duration

Entry Type Calculated

Description The Finish Slack field contains the duration between the Early Finish and Late Finish dates. The smaller of the finish slack and start slack amounts determines the amount of free slack available, that is, the amount of time a task can be delayed without affecting the start date of a successor task or the project finish date.

How Calculated Finish slack is the duration that represents the difference between the late finish and early finish dates. The early finish is the earliest date that a task could possibly finish. Likewise, the late finish field contains the latest date that a task can finish without delaying the finish of the project. Project calculates the finish slack as follows:

Finish Slack = Late Finish - Early Finish

Best Uses Add the Start Slack and Finish Slack fields to any task view when you want to review how free slack was calculated.

Example You are reviewing free slack in your schedule and want to see more details about how it was calculated. You add the Start Slack and Finish Slack fields to the task sheet and analyze the durations.

Remarks If a task has an actual start date and also a deadline set, the start slack will be 0 and the finish slack will be the difference between the task’s finish date and deadline date.
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Tue, 2009-11-17 17:21
#11
Bryan Eaton
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I am clearly not understanding how MSProject works here...

I posted an example of what I have MSProject Rollup Float Not Working as expected

The column titled "TF" is my Custom Duration1 set to [Finish Slack] and Rollup to minimum. My expectation was for it to display the smallest amount of float/slack of the subordinate tasks in the summary ie ’0’, I dont understand where the 14 comes from?

Clearly the last activity in the group with 418 days slack is not connected to anything and will be dealt with.
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Tue, 2009-11-17 18:21
#12
Trevor Rabey
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Any Deadlines set?
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Tue, 2009-11-17 21:37
#13
Bryan Eaton
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After a lot of trial and error, it turns out all I needed to do was hit the F9 button. Thanks to Trevor for prompting me to set the deadline, as otherwise I would probably not have tried the F9.

The relationship types have no bearing on this particular issue, I am sure the discussion is held in other forum postings.

The variety of duration units is due to my customers needs - Project Managers, Directors and the like - seeing it as easier to read a schedule as 8 months rather than 160 days for instance. We schedulers can live with the hardship of comparing disparate units. Although it is apparent that using the Custom Duration field gets around this, as all durations are expressed in days...

So my workaround is now fixed, but the original question of how to manage MSP to give the right answer stands - any halp is greatly appreciated.
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