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Problem with Multiple Calendars and Float

7 replies [Last post]
Rob Lillico
User offline. Last seen 7 years 7 weeks ago. Offline
Joined: 6 Jul 2012
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Study the following activity table and Gant chart, all the necessary information should be there. The calendar for activity A has continuous working days. The calendar for activities B and C is for a 10 days on 4 days off roster.

1233
problem_with_multiple_calendars_and_float_a.png

1234
problem_with_multiple_calendars_and_float_b.png

Note that the end date will not be pushed out unless over 2 days duration is added to activity A. This means that activity A should have 2 days float.

Why then does activity A have a float of negative 2 days?

(hopefully the picture isn't too small)

Replies

Rafael Davila
User offline. Last seen 1 hour 30 min ago. Offline
Joined: 1 Mar 2004
Posts: 4784

It might be an issue with the lag calendars, unfortunately P6 is limited to some global control of lag calendars instead of an independent calendar. Sometimes you need it to be equal to successor, sometimes you need it to be equal to predecessor and sometimes different to successor or predecessor but not a 24/7 calendar.

  • Predecessor Activity Calendar - Choose this option to calculate lag based on the predecessor activity's calendar.
  • Successor Activity Calendar - Choose this option to calculate lag based on the successor activity's calendar.
  • 24 hour calendar - Choose this option to use a calendar that specifies work time 7 days/week and 24 hours/day.
  • Project Default Calendar - Choose this option to use the calendar that is designated as the default for new activities.
  • The default calendar for new activities is specified on the Administration > Calendars page or in the Project Management module.

Suggest you try changing the options and see if the computed values of float varies.
Also try changing the milestone type from finish to start milestone. 

Gary Whitehead
User offline. Last seen 19 weeks 4 days ago. Offline

It seems to be calculating the late finish of Activity A using Activity B's calendar, for some reason.

 

Can you try a couple of things for me?

(1) Please confirm relationship from A to B is FS with zero lag

(2) Please confirm what settings you have in schedule options for "Compute Total FLoat As" and "Calendar for scheduling relationship lag"

(3) What happens to total float if you change the settings in (2)?

(4) What happense to total float if you make activity B a start milestone?

(5) What happens if you make it a task?

(6) What happens if you dissolve activity B?

(7) What happens if you give Activity B (as a finish milestone) the continuous calendar?

Daniel Limson
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Rob,

In P6, the default number of hours per day is 8 hours = 1 day, the moment you change the working hours then the calculations will change.

Regards,

Daniel

Rob Lillico
User offline. Last seen 7 years 7 weeks ago. Offline
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That is correct, if I had the same calendar for all my activities, the total float of each of my critical path activities would be zero. I think this may be a bug.

Rob Lillico
User offline. Last seen 7 years 7 weeks ago. Offline
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There are no constraints on any of the activities except for the first one (A) which has a "Start on or After" primary constraint.

Check if there are no Finish No Later han constrints.

Anoon Iimos
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Joined: 22 Sep 2006
Posts: 1416

I can only guess that it's because of the difference in calendars;

and the links as FS for all;

if you got the same calendar for all,

then your total float will be zero