Start and Finish VS Total Duration

[Robert H]

I have a project with Summary tasks and tasks and at this point no
resources assigned. We are estimating tasks duration and entering them
on sub tasks. We trying to look at overall duration. I’ve noticed
that the Duration Field (column) calculates duration as duration of
worked days and does not simple look at Finish – Start for an
“overall” duration. I set up a custom duration field “Total Duration”
with the formula ProjDateDiff([Start],[Finish]) which I proofed by
comparing with Finish – Start date calculations in Excel. However,
some summary tasks show zero days in the custom Total Duration field
even though there are days (many) in the respective start and finish
fields.
I’m lost as to why this is happening. Hopefully someone can point me
in the right direction.
Robert

 

[Steve House]

It's happening because that is the textbook definition of "duration" as
being the number of working time units between when the task/project begins
and when it ends. intervening non-working times - evenings, weekends,
lunchbreaks, etc on the standard calendar - simply don't count for duration.
A task starting Monday at 8am and ending Friday at 5pm has a duration of 40
hours, not the total time difference of 105 hours. What you are describing
is "elapsed time," a totally different measure. The reason for the
distinction is obvious when you think about it - progress on a project is
driven by resources doing work and work can only take place when the
resource is physically present and able to do it. So as far as measuring
what time frame will be required to complete a certain body of work, the
only time measurements that matter are the times when resources are able to
work, ie, time defined by the working-time calendar. Progress will be zero
during non-working time. When building work schedules that will complete
the deliverable in the shortest possible time, which is what Project is for,
the only thing that matters is available working time. Elapsed time will
always be greater than or equal to duration, usually greater since it is a
rare task that does not have at least some non-working time occuring between
its beginning and ending.
--
Steve House [Project MVP]
MS Project Trainer & Consultant
Visit http://project.mvps.org/faqs.htm for the FAQs



I have a project with Summary tasks and tasks and at this point no
resources assigned. We are estimating tasks duration and entering them
on sub tasks. We trying to look at overall duration. I've noticed
that the Duration Field (column) calculates duration as duration of
worked days and does not simple look at Finish - Start for an
"overall" duration. I set up a custom duration field "Total Duration"
with the formula ProjDateDiff([Start],[Finish]) which I proofed by
comparing with Finish - Start date calculations in Excel. However,
some summary tasks show zero days in the custom Total Duration field
even though there are days (many) in the respective start and finish
fields.
I'm lost as to why this is happening. Hopefully someone can point me
in the right direction.
Robert

 

[Jim Aksel]

I'm going to go out a limb here and make the assumption none of your summary
tasks are calculating correctly. Check to be sure you have the formula set
for the summary bars as well.

Right click on your custom duration column, select "Customize Fields..."
In the second grouping down, it says "Calculation for task and group summary
rows", make sure you have the "use formula" radio button checked.

Also, when I use the ProjDateDiff() function, the result I get is a delta of
work days not elapsed days as you suggest. Try using this formula in a spare
Number column:
DateDiff("d",[Start],[Finish])+1. The following also works (in a number
field): ([Finish]-[Start])+1

Let us know if this helps

--
If this post was helpful, please consider rating it.

Jim

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

 

[Robert H]

Steve, thanks for the concise explanation of Duration and its relation
to Elapsed Time. Ive read alot of help info and FAQs but your
description is the only one that "clicked"...
Ive changed my custom field to "Elapsed Time". It helps me relate my
project to the rest of the world.
Robert

 

[Robert H]

Jim, you were right I did need to select the "Calculation for task and
group summary
rows", "use formula" button. ([Finish]-[Start])+1 worked perfect,
the first formula did not work.
Thank You Very Much
Robert


O([Finish]-[Start])+1n May 30, 12:46 pm, Jim Aksel

I'm going to go out a limb here and make the assumption none of your summary
tasks are calculating correctly. Check to be sure you have the formula set
for the summary bars as well.

Right click on your custom duration column, select "Customize Fields..."
In the second grouping down, it says "Calculation for task and group summary
rows", make sure you have the "use formula" radio button checked.

Also, when I use the ProjDateDiff() function, the result I get is a delta of
work days not elapsed days as you suggest. Try using this formula in a spare
Number column:
DateDiff("d",[Start],[Finish])+1. The following also works (in a number
field): ([Finish]-[Start])+1

Let us know if this helps

--
If this post was helpful, please consider rating it.

Jim

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

I have a project with Summary tasks and tasks and at this point no
resources assigned. We are estimating tasks duration and entering them
on sub tasks. We trying to look at overall duration. I’ve noticed
that the Duration Field (column) calculates duration as duration of
worked days and does not simple look at Finish – Start for an
“overall” duration. I set up a custom duration field “Total Duration”
with the formula ProjDateDiff([Start],[Finish]) which I proofed by
comparing with Finish – Start date calculations in Excel. However,
some summary tasks show zero days in the custom Total Duration field
even though there are days (many) in the respective start and finish
fields.
I’m lost as to why this is happening. Hopefully someone can point me
in the right direction.
Robert

 

[salgud]

It's happening because that is the textbook definition of "duration" as
being the number of working time units between when the task/project begins
and when it ends. intervening non-working times - evenings, weekends,
lunchbreaks, etc on the standard calendar - simply don't count for duration.
A task starting Monday at 8am and ending Friday at 5pm has a duration of 40
hours, not the total time difference of 105 hours. What you are describing
is "elapsed time," a totally different measure. The reason for the
distinction is obvious when you think about it - progress on a project is
driven by resources doing work and work can only take place when the
resource is physically present and able to do it. So as far as measuring
what time frame will be required to complete a certain body of work, the
only time measurements that matter are the times when resources are able to
work, ie, time defined by the working-time calendar. Progress will be zero
during non-working time. When building work schedules that will complete
the deliverable in the shortest possible time, which is what Project is for,
the only thing that matters is available working time. Elapsed time will
always be greater than or equal to duration, usually greater since it is a
rare task that does not have at least some non-working time occuring between
its beginning and ending.

This is the most complete, yet succint, explanation of this aspect of
Project I can remember reading. Thanks, Steve!