Duration in Summary Tasks

[JenPrl]

It's not adding up like i'd like it to...I have a project that requires the
the summary tasks duration to be the summation of its subtasks... I cannot
figure out how to get duration to be this simple summation... This is a
project where all duration is done in hours...

 

[Nandakumar Sankaran]

Can you describe this situation in more detail?

Nandakumar

 

[John]

JenPrl,
Project is working correctly. Don't think of a Summary line as a task
because it is not. Rather it is "summary" (not a summation) of its
subtasks. Therefore Duration at a summary level is simply the difference
in working time (usually expressed in days) between the Start date of
the earliest subtask and the Finish date of the latest subtask. If for
some reason you want a sum of Durations for all subtasks, use a custom
field (e.g. Duration1) and a formula to sum up the values.

One exception (if you can call it that) to the above is that if all
subtasks under the Summary line are linked finish-to-start with no lead
or lag, then the Summary line Duration should equal the sum of the
subtask Durations. If this is your case and that isn't happening, I'd
check all the links and make sure there are no subtasks in parallel.

Hope this helps explain.
John

 

[Steve House]

John's answer is right on the money but a question popped into mind. When
you say you need to sum the durations into the summary task, it makes me
wonder if you might be really thinking of man-hours of work rather than
working hours of duration when you are entering your task durations. Even
though both measures use the units "hours" they really are two entirely
different concepts and are NOT interchangeable. The duration is, as John
pointed out, the time when work could have taken place place between when a
task (or summary) begins and when it's done, regardless of whether or not
someone was actually doing something every minute. The total duration of
3 8-hour tasks all taking place on the same day is 8 hours, not 24 because
even though we had 3 tasks going on, work began on all of them at 8am and
finished at 5pm on the same day, running for just 1 8-hour period of time.
Work, OTOH, is the total amount of working time the resources are actively
putting in on the task.

Answer for yourself this question: I have 1 task that runs the full 8 hour
workday and has 3 people working together all day on it. Would you enter
that task as an 8 hour task or a 24 hour task? If it's 8 you're working
with duration but if it's 24 you're actually dealing with work. As John
said, durations aren't additive and the summary duration is not the total of
the subtasks. Work, OTOH, is additive and the work in the summary is the
total of the subtasks. Be careful you keep them straight and don't
mix-and-match.

 

[John]

JenPrl,
No need to set anything up - it's already there. As long as the Work
field is shown in the view, the Work hours at the Summary Line level
will be the algebraic sum of Work hours for the subtasks. You do however
need to have Tools/Options/Calculation tab set for automatic.

John

 

[Steve House]

Adding again to John's comments - make absolutely sure you're not
inadvertently entering work estimates into the duration fields when you
build your task list. Sometimes they are equal but other times they're not.
Be sure you always enter apples for apples ...
--
Steve House [MVP]
MS Project Trainer/Consultant
Visit http://www.mvps.org/project/faqs.htm for the FAQs

 

[Mike Glen]

Come on, JenJenPrl! Every entry in Project can only be an estimate. The ?
is an extra to allow you to simply be alerted to Durations (not work) that
need to be firmed up later, and Project allows a filter specifically to
highlight tasks with estimated Durations.

Mike Glen
Project MVP

wrote:

 

[John]

JenPrl,
No, I'm not the best. I'm just a regular guy who knows enough to be
truly dangerous

Good luck.
John

 

[Steve House]

Nope - the work is the amount of effort the resource will expend. The
duration is the amount of time over which he will expend it. The "?"
indicates an estimated duration, NOT an estimated work, because the duration
field is a time measurement, not a work measurement. Remember that "work"
in MS Project is what is called "effort" in most other project management
contexts to better indicate it is not a time measurement. (Project, OTOH,
uses the term "effort" to indicate the rate at which work is performed.) Of
course, all durations are estimates until the work is actually done but I
think of the question mark as a reminder flag telling me I should come back
and take another look at that task's timing when I have more information to
go on.

The difference between a work estimate and a duration estimate is
illustrated by the difference between work and duration itself. I have a
task that requires 40 man-hours of work. If my resource devotes his full
attention to it he'll do it over the course of 40 hours of duration. But he
might be juggling two things at once and is only able to devote half his
energy to this particular task. He still has to generate 40 man-hours worth
of output, but now it'll take him twice as long. 40 man-hours of work at
50% effort means 80 hours of duration. Or maybe he's working full speed and
I get another guy to work alongside him. Now the total effort applied to
the task is 200% (2 people @ 100% each) and the 40 man-hours of work gets
done in 20 hours of duration because we get 2 hours of work output for each
hour of time put in.

If you make an analogy to a trip in a car, work is the distance to be
traveled, effort (assignment %) is the speed you're going, and duration is
the time it takes to get there.

--
Steve House [MVP]
MS Project Trainer/Consultant
Visit http://www.mvps.org/project/faqs.htm for the FAQs