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Must Start on

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Mon, 2017-05-15 13:41
moutaz aldeib
User offline. Last seen 3 years 5 weeks ago. Offline
Joined: 31 Dec 2003
Posts: 291
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Hi Planners,

A baseline schedule showing that the start date of the project "milestone task" is not critical "9 days float", some of the succesor tasks has a constraint "start no earlier than". I changed the constraint of those successors to "Must start on" and I got the start date critical. Is there any explanation to this?

Regards,

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Mon, 2017-05-15 16:05
#1
Tom Boyle
User offline. Last seen 11 weeks 1 day ago. Offline
Joined: 28 Nov 2006
Posts: 304
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Moutaz,

Look closely at the early and late dates of your affected tasks.

  1. According to your description (and ignoring other impacts), at least one of your successor tasks already has a logic-driven early start date that is 9 days later than its SNET date. 
  2. SNET constraints on the successor tasks only have the potential to affect their early dates - with no effect on your project start milestone.
  3. By changing the SNET constraints to MSO, you are completely over-writing both the early dates and the late dates on those tasks.  The backward pass carries this effect back to the late dates of your project start milestone.

MSO/MFO constraints in MSP are similar to Mandatory constraints in P6.  I avoid them in general.  If Total Slack or the "Critical" flag is to be relied on, then you must never assign them to any logically-connected task.  I wrote more about this last year: http://wp.me/p6CCB4-7w

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