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Calculation of Duration on fixed work tasks for multiple resources
Question

WBS
Task Name
Work
Duration
Start
Finish
Resource Names
1
test task  fixed work
33 d
30 d?
2/1/12
3/12/12
test1[70%],test 2[55%]
2
test task 2  fixed work
33 d
26.4 d?
2/1/12
3/6/12
test1[125%]
3
test task  fixed duration
37.5 d
30 d
2/1/12
3/12/12
test1[70%],test 2[55%]
4
test task 2  fixed duration
33 d
26.4 d
2/1/12
3/6/12
test1[125%]
In tasks 1 and 2 I have the Task Type set to Fixed Work because I want to enter the effort estimate in the Work field and the resources and have Project tell me the Duration. Task 1 has 2 resources assigned at 70% and 55% respectively. To my mind that equals 125% of 1 FTE. Task 2 has 1 resource assigned at 125%. As you can see MS project calculates the Duration differently. I think these 2 tasks should calculate the same Duration but they don’t.
In tasks 3 and 4 I have the Task Type set to Fixed Duration with the Effort flag turned off. I then assigned the Duration fields equal to tasks 1 and 2. Finally I assigned the same resources as tasks 1 and 2. As you can see task 4 calculated the correct work as expected. Task 3 calculated a higher work than task 1 but this appears to be calculated correctly given the 125% FTE assignment.
Answers

GD Projects,
No error in calculations. The best way to see what happens is to look at the Resources Usage view. When you initially assign multiple resources to a fixed work task, Project automatically splits the total work equally. Therefore, for task 1 the total work content is 264 h (33d). Each resource is allocated one half of that or 132 h each. Now, test1 is assigned at 70% so each day he works 5.6h. Test2 is assigned at 55% so each day he works 4.4h. Since text1 is working more hours on that task each day, he finishes his 132 hours sooner. Test2 then completes his 132 hours several days later for a total duration of 30d.
Task 2 is a little different. Test1 has all 264h. He works overtime at the rate of 10h/d and therefore is able to complete the task in 26.4d.
Task 3 follows a slightly different "plan". We know from the above that for 2 resources on the task, test1 works 5.6h/d and test2 works 4.4h/d. However, since the task is now fixed duration, they each work the full 33 days. Hence the total work content is 300 hours (37.5d).
Task 4 follows essentially the same work plan as task 2.
Hope this helps.
John
 Marked as answer by GD Projects Tuesday, February 7, 2012 9:18 PM

GD Projects,
You're welcome and thanks for the feedback. A little bit more reading is in order to understand how Project implements the work equation for each task type and how it differs between initially making the resource assignment and making a change once the task is set up. For the basics on that see, http://office.microsoft.com/enus/projecthelp/changethetasktypeprojectusestocalculatetaskdurationHP010092039.aspx
In Project 2010, the way assignment units is handled changed. For a blog article on those changes see, http://blogs.msdn.com/b/project/archive/2010/04/29/assignmentunitsinproject2010.aspx
Hope this helps.
John
 Marked as answer by GD Projects Wednesday, February 8, 2012 12:26 AM
All replies

GD Projects,
No error in calculations. The best way to see what happens is to look at the Resources Usage view. When you initially assign multiple resources to a fixed work task, Project automatically splits the total work equally. Therefore, for task 1 the total work content is 264 h (33d). Each resource is allocated one half of that or 132 h each. Now, test1 is assigned at 70% so each day he works 5.6h. Test2 is assigned at 55% so each day he works 4.4h. Since text1 is working more hours on that task each day, he finishes his 132 hours sooner. Test2 then completes his 132 hours several days later for a total duration of 30d.
Task 2 is a little different. Test1 has all 264h. He works overtime at the rate of 10h/d and therefore is able to complete the task in 26.4d.
Task 3 follows a slightly different "plan". We know from the above that for 2 resources on the task, test1 works 5.6h/d and test2 works 4.4h/d. However, since the task is now fixed duration, they each work the full 33 days. Hence the total work content is 300 hours (37.5d).
Task 4 follows essentially the same work plan as task 2.
Hope this helps.
John
 Marked as answer by GD Projects Tuesday, February 7, 2012 9:18 PM


GD Projects,
You're welcome and thanks for the feedback. A little bit more reading is in order to understand how Project implements the work equation for each task type and how it differs between initially making the resource assignment and making a change once the task is set up. For the basics on that see, http://office.microsoft.com/enus/projecthelp/changethetasktypeprojectusestocalculatetaskdurationHP010092039.aspx
In Project 2010, the way assignment units is handled changed. For a blog article on those changes see, http://blogs.msdn.com/b/project/archive/2010/04/29/assignmentunitsinproject2010.aspx
Hope this helps.
John
 Marked as answer by GD Projects Wednesday, February 8, 2012 12:26 AM