Summary Task Duration Incorrect

[Engineer]

I have entered a series of FS tasks using durations in hours and a resource
that has a 24/7 calendar. If I add up the total task duration manually it is
173 hours. But the summary task directly above these tasks shows 5.5 days.
It should be 7.2 days (173 / 24 = 7.208). Any suggetions why this is coming
out wrong? I also tried using elapsed hours instead of hours and have the
same incorrect summary task duration.

 

[John]

I have entered a series of FS tasks using durations in hours and a resource
that has a 24/7 calendar. If I add up the total task duration manually it is
173 hours. But the summary task directly above these tasks shows 5.5 days.
It should be 7.2 days (173 / 24 = 7.208). Any suggetions why this is coming
out wrong? I also tried using elapsed hours instead of hours and have the
same incorrect summary task duration.

Engineer,
Project is calculating the summary line duration as 5.5 days because the
setting under Tools/Options/Schedule hours per day is still set at 8.
Furthermore, even though you may have the resource calendar set for
24/7, my guess is that the project calendar is still standard (i.e.
8/5). If you change the hours per day setting to 24 AND change the
project calendar to a 24 hour calendar, the summary line will display a
duration of 7.21 days.

Hope this helps.
John
Project MVP

 

[Engineer]

Thanks for the input.

I don't want the entire project to run 24/7, just a small section of the
project (which I have indented to create a summary task).

With 173 hours total, and 8 hours / day, wouldn't it calculate that out to
be 21.62 days?

This section of my project has 9 consecutive tasks (finish-to-start) as
follows: 24 hours, 16h, 3h, 20h, 6h, 24h, 16h, 60h, 4h. Totalled that is 173
hours. 173/24 = 7.2 days.

Project is saying 5.5 days in the duration of the summary task. That would
imply there are 31.45 hours per day. (173/5.5=31.454)

That does not make any sense to me.

Any other suggestions would be approciated.

 

[John]

Thanks for the input.

I don't want the entire project to run 24/7, just a small section of the
project (which I have indented to create a summary task).

With 173 hours total, and 8 hours / day, wouldn't it calculate that out to
be 21.62 days?

This section of my project has 9 consecutive tasks (finish-to-start) as
follows: 24 hours, 16h, 3h, 20h, 6h, 24h, 16h, 60h, 4h. Totalled that is 173
hours. 173/24 = 7.2 days.

Project is saying 5.5 days in the duration of the summary task. That would
imply there are 31.45 hours per day. (173/5.5=31.454)

That does not make any sense to me.

Any other suggestions would be approciated.

Engineer,
Unfortunately Project does not have the flexibility to customize how
durations are calculated for different groups of tasks. You could use
VBA and a spare field to effect this customization but I have a better,
easier suggestion - leave all durations in hours. And no, customizing
the spare field with a formula will not work because a formula will
apply equally to ALL task lines, unless you create a more complex
formula that queues on a flag of some type.

John
Project MVP

 

[DavidC]

Hi Engineer,

The answers are essentially correct. The summary task looks at the start
and end date and calculates the duration based on it's calendar. So if the
calendar has weekends as non working then a 7 day task ona 24/7 calendar will
show up as 5 days. Quite simple, the calendar for the summary task does not
recognise the weekend as working. Also the calnedar for the summary task
will likely be set to only have 8 hour days, so the combination of the
difference in working houirs and days per week, gives a different resulting
duration. Try it with a sample summary task with one task set on a 24 hour
calendar and give it 7 days. Then go to the summary task, and set that
calendar to 24 hours and you will see that they match.

Also note that unless the underlying tasks are exactly sequential with no
negative or positive lags, then the summary task duration will never equal
the sum of the parts.

The summary task is merely calculating from start to finish based on its own
calendar setting and will not necessarily match the apparent total of the
underlying tasks.


Hope this helps a little.

Regards

DavidC