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Duration calculation issue
Question

Hi!
I have a project where one of the resources works 5 hours/day, so I adjusted the available time for only this resource.
Then I started to create tasks as follows:
Task1  Fixed duration  Duration: 3 days
Task2  Fixed work  Work: 20 hours
Task3  Fixed work  Work: 5 hours
When I assigned the resource to Task1, MS Project recalculated the work correctly as 15 hours (3 days x 5 hours/day), then I assigned the same resource to Task2 and the duration calculated was 2.5 days. It seems that Project ignored the fact that the resource assigned has only 5 hours/day of work to calculate the duration, but It considered this information previously to calculate the work for Task1
Is it a bug or am I doing something wrong and expecting Project to correct me? Any suggestions on how to fix it?
Answers

Cassanti,
You're not doing anything wrong in your setup and MSP is not calculating wrongly either (i.e. no bug).
What is wrong is what you expect to see as a result. A day is still defined as 8 hours in your schedule and the definition of what a day is can't change just because the resource calendar change. Therefore the 20 hrs equals 2.5 days, but I bet if you look at your start and finish dates, the difference will be 4 days for task 2.
You can change the definition of a day to being 5 hrs, but then you will just have problems with resources that work the normal 8hrs/day (or some other resource calendars).
One solution could be to let the "Duration"column show the duration in hours instead of days and the correct result will be shown, but I admit it is sometimes not the best. Otherwise insert a custom duration field that calculates difference between finish and start dates.
The solution with max units also works, even though it IMO distort the picture of when the resource is actually at work. With a limit of max units being 62.5%, the resource will still work 8 hrs every day, but only 37.5 min./hrs. The full day can be seem if adding the timeunit to dates. Correct that actual work is 5 hrs/day, but he/she at the job site for 8 hrs/day (or whatever the main calendar may be).
The funny thing with the 62.5% is that if you enter it in % it will result in the correct days, being 4, but if you enter it in decimals (0.625) it will round of to 0.63 and the final result will be 3.97 days. That could be a bug.
Regards,
BJ
 Marked as answer by Cassanti Friday, January 18, 2013 1:45 PM
All replies

Cassanti,
Probably doing something wrong. How did you set up the resource for 5 hours/day?
Here's what I did. If the resource only works 5 hrs/day in a normal 8 hour work day, then his/her max units should be 5/8=62.5%, which is entered in the Max Units field on the Resource Sheet. If that resource is then assigned to a fixed work task and the work content (i.e. Work field) is 20 hours, Project will correctly set the duration at 4 days.
John

Cassanti,
You're not doing anything wrong in your setup and MSP is not calculating wrongly either (i.e. no bug).
What is wrong is what you expect to see as a result. A day is still defined as 8 hours in your schedule and the definition of what a day is can't change just because the resource calendar change. Therefore the 20 hrs equals 2.5 days, but I bet if you look at your start and finish dates, the difference will be 4 days for task 2.
You can change the definition of a day to being 5 hrs, but then you will just have problems with resources that work the normal 8hrs/day (or some other resource calendars).
One solution could be to let the "Duration"column show the duration in hours instead of days and the correct result will be shown, but I admit it is sometimes not the best. Otherwise insert a custom duration field that calculates difference between finish and start dates.
The solution with max units also works, even though it IMO distort the picture of when the resource is actually at work. With a limit of max units being 62.5%, the resource will still work 8 hrs every day, but only 37.5 min./hrs. The full day can be seem if adding the timeunit to dates. Correct that actual work is 5 hrs/day, but he/she at the job site for 8 hrs/day (or whatever the main calendar may be).
The funny thing with the 62.5% is that if you enter it in % it will result in the correct days, being 4, but if you enter it in decimals (0.625) it will round of to 0.63 and the final result will be 3.97 days. That could be a bug.
Regards,
BJ
 Marked as answer by Cassanti Friday, January 18, 2013 1:45 PM

Hi basejump!
Thank you for the clarification! It was quite what I expected to hear (read).
You are correct. Though Project calculates 2.5 days duration, the difference between the start and finish dates is exactly the 4 days I'm looking for.
I will go for the custom field solution, this way I don't have to change or distort any information and still see what I want to see.
Thank you very much!
Regards.