Fixed units question

[April]

Please can you clarify how the Units are calculated when Fixed Work is
selected. For example the scenario is : 20 days duration, 8 hours per day
and 80 hours Fixed Work. I know the answer is 50% but how is this
calculated?

Thanks you
Kind regards.

 

[Rob Schneider]

Please can you clarify how the Units are calculated when Fixed Work is
selected. For example the scenario is : 20 days duration, 8 hours per day
and 80 hours Fixed Work. I know the answer is 50% but how is this
calculated?

Thanks you
Kind regards.

20 days duration = 20 x 8 = 160 hours duration
80 hours of work spread across 160 hours duration
so
80/160 = 0.5 units of work on each of the 20 days, e.g. 1/2 time.

 

[April]

Thanks.

So does that mean 0.5 x 8hours=4 hours which is 50%..... my maths is a bit
rusty. How is that bit calculated...?

 

[Steve House [MVP]]

You can kind of think of Units as representing the rate work is performed.
Most tasks are fixed work because most tasks require the completion of a
specific physical deliverable - you have to make X number of widgets, no
more and no less, when doing this task. Perhaps I'm painting a wall and can
paint 10 square feet and hour when I going at full speed. But if I'm
talking about the World Cup with my buddy as I paint I won't go full speed
and will only get 5 square feet done per hour. I'm on the painting task at
50%. The wall doesn't get any bigger or shrink smaller with my assignment.
So if I could have finished the room in 1 day normally, during the
tournament it's going to take me 2 days.

 

[Rob Schneider]

April,

See Steve's reply who elaborates on this for you.

 

[tonyzink]

Hi April --

Here is the formula that is used in the MSProject scheduling engine to
calculate Work, Duration, and Units for a task:

Work = Duration x Units

....or if we don't know the Units, we can re-work the formula with
simple algebra to read:

Units = Work / Duration

So, for example, if we substitute your values into the formula:

Units = 80hrs Work / 20days Duration

....but this doesn't quite work, so we'll change the duration from
20days to 160hrs (8hrs per day):

Units = 80hrs work / 160hrs Duration
Units = 0.5

....or...

Units = 50%

This formula (Work = Duration x Units) applies to all tasks,
regardless of the selected task type:

....Fixed Units
....Fixed Work
....Fixed Duration

If you know 2 of the 3 variables (Work, Duration, or Units), then you
can use the formula to determine the missing variable (this is what
MSProject does for you). The selected task type (Fixed Units, Fixed
Work, and Fixed Duration) only comes into play when you somehow
manipulate a task. If you have a task which already has all 3 variables
set, but then you decide to change something, then the task type will
determine how the task behaves after the change is made.

For example, if we have a Fixed Work type of task and we've established
the following:

0.5 Units = 80hrs Work / 160hrs Duration

....then we know that the Work variable cannot change (it's fixed), and
if we change the Units from 0.5 to 0.8 (meaning that we've decided to
work on the task 80% of the time, rather than 50% of the time):

0.8 Units = 80hrs Work / new Duration

How long (new Duration) will this 80hr (Work) task take, now that we've
decided to work on it 80% of the time? Let's re-work our formula a bit:

Duration = 80hrs Work / 0.8 Units
Duration = 100 hrs

....converting from hours to days:

Duration = 12.5days

Clear as mud?

Good luck!

Tony Zink
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