What causes duration to change

[ltaylor57]

I just setup a new project plan. After adding resources I noticed that my
durations have changed. Sometimes they are minor (changing from 5 to 4.5,
etc) but in other cases more significant. What can cause a duration to change

 

[Jim Aksel]

Work = Units% x Duration

Tasks may be one of three types: Fixed units (default), fixed work, fixed
duration.
In the above equation, project holds one of the items constant depending on
the task type. Now this becomes a math problem.

One other wrinkle, fixed units and fixed duration tasks may be effort driven
or not. Depending on the checked or unchecked status of the effort driven
parameter, adding more resources will either (1) Redistribute the remaining
work among all the resources including the new ones. (2) Add more work in
accordance with the units% for all the resources assigned.

By default, project sets a task to Fixed Units. So, if you create a 5
datask and assign 1 resource to it you get 40 hours of work. Fixed units is
100%, Effort Driven. These are the defaults. Then you decide this is a 20
hour task (do not confusion work with duration).... you change the work to
20 hours.

Since units% is fixed at 100%... it only takes 2.5 days for a fully
dedicated resource to expend 20 hours of work.

Does that help?
--
If this post was helpful, please consider rating it.

Jim Aksel, MVP

Check out my blog for more information:
http://www.msprojectblog.com

 

[ltaylor57]

I thought duration was the amount of time estimated to complete the task.
Whats the best way to accomplish setting a specific number of hours for a
task and NOT have project adjust them?

 

[Projectability]

You can try "Fixed Work" as your default task type - it can be changed for
existing tasks on the Advanced Tab of the Task Info dialogue box and can be
set as default for all new tasks from the Tools>Options>Schedule tab.

Be aware that with Fixed Work scheduling if you vary resource input there
will be an inverse impact on the duration - reduced % allocation means
increased duration and vice versa. Also if you add extra resource the work
is shared proportionately and the duration reduces accordingly.

--
Dominic Moss

Projectability - Helping People achieve more with Microsoft Project

www.projectability.co.uk