Adding resource to a fixed-duration, effort-driven task

[JNB]

Hi all,

I create the following task:

Duration: 5 days, Type: Fixed-duration
Effort-driven scheduling: Yes
Initial resource assignment:
Resource #1, 50% Project calculates 20h of work
Resource #2, 50% Project calculates 20h of work

Suppose I decided to increase the total work on the task by assigning
additonal
resources. When I try to assign another resource with 50% of assignment
units, I get the warning message:
"Project cannot create an assignment with a specific unit value on a fixed
duration,
effort-driven task. Once the assignment is created, you can edit the unit
value on
the assignment"

On the other hand, it works if I assign Resource #3 with 100%, adding an
extra 40h of work; then I change it to 50%.

It also works if I enter 20h into the Work field for Resource #3; Project
calculates Units as 50%.

Alternatively, I can turn effort-driven option off, assign the resource and
then
turn it on back.

My purpose is not to find a workaround or define the task with the right
task type
(probably fixed work), instead I just want to understand how it works.

Why do I get the warning message ?
I am sure Project's behaviour is consistent with scheduling algorithm but I
need
some help with figuring out what the logic behind is. Thanks in advance for
any insight.

 

[Steve House]

The message is due to the behavior of an effect driven task in general.
Adding a resource to an effort driven task does not increase the total work;
adding one to a non-effort driven task does. You have your two resources
each doing 20 man-hours of work for a total of 40 manhours required for the
task. Effort driven means that when you add another resource, the total
work does NOT increase but rather the 40 hours is redistributed amongst the
group of now 3 resources. The effort driven parameter says that each
resource should now have 13.33 man-hours hours of work., each of them now
assigned at 33%, reducing the allocations of the first 2 resources in the
process. But specifying your assignment percentage of 50% on a 5-day fixed
duration task (instead of letting Project calculate it from the duration and
the hours of work) says the new guy should get 20 hours - the message is
saying you are asking Project to simultaneously to do two things that are in
conflict with each other - give him 13.3 hour and also give him 20 hours -
and it can't do both. The best solution is simply to switch off the effort
driven setting before adding the new guy. I suggest that the effort driven
and task type settings are not engraved in granite - they are switches that
you use when editing assignments so that Project does the correct
calculation for the edit you are making at the moment. The settings for a
given task could potentially be changed many times as a project plan evolves
as you make different edits for different purposes.

 

[JNB]

There was a similar discussion on the topic and I’ve also read it before
posting my
question (Archive ref: your reply on 2/3/2006 9:05:11 AM Re: Effort driven
fixed
duration task).

I will follow the procedure that you suggested. Thank you. I really appreciate
your help.

---
Best Regards - JNB

The message is due to the behavior of an effect driven task in general.
Adding a resource to an effort driven task does not increase the total work;
adding one to a non-effort driven task does. You have your two resources
each doing 20 man-hours of work for a total of 40 manhours required for the
task. Effort driven means that when you add another resource, the total
work does NOT increase but rather the 40 hours is redistributed amongst the
group of now 3 resources. The effort driven parameter says that each
resource should now have 13.33 man-hours hours of work., each of them now
assigned at 33%, reducing the allocations of the first 2 resources in the
process. But specifying your assignment percentage of 50% on a 5-day fixed
duration task (instead of letting Project calculate it from the duration and
the hours of work) says the new guy should get 20 hours - the message is
saying you are asking Project to simultaneously to do two things that are in
conflict with each other - give him 13.3 hour and also give him 20 hours -
and it can't do both. The best solution is simply to switch off the effort
driven setting before adding the new guy. I suggest that the effort driven
and task type settings are not engraved in granite - they are switches that
you use when editing assignments so that Project does the correct
calculation for the edit you are making at the moment. The settings for a
given task could potentially be changed many times as a project plan evolves
as you make different edits for different purposes.