Hi,

as you know the Magic formula is DURATION * UNITS = WORK!

But there is a change in MS PROJECT in representing this field.

I made a setup for this Post! I have three Tasks, each of them has one Resource assigned. Task 1 is Fixed Unit, Task 2 is Fixed Work, and Task 3 is Fixed Duration.

I will change each of this Values (Units, Work, and Duration), for each Tasks type. Notice that I put additional field in Task Usage View, called Peak:

First I will make changes for Task 1.

I will change Duration from 2 days to 4 days an I will get:

According to formula, Units are fixed so Duration * Units = Work, e.g. 4 days (4*8 hours per day = 100% * 32 hours). So Work is changed from 16 to 32 hours.

I will change Work from 16 to 24 hours now, and I will get:

According to formula, Units are fixed so Duration * Units = Work, e.g. Duration *100% = 24 hours = 24 hours / 8 hours per day = 3 days. So Duration is changed from 2 to 3 days.

I will change Units from 100% to 200%, and I will get:

According to formula, Duration * Units = Work, e.g. Duration * 200% = 16 hours = 16 hours / 200% = 8 hours = 1  day, because Resource will work with 200% capacity instead of 100% . So Duration is changed from 2 days to 1 day.

Now I will make changes for Task 2 (Fixed work).

I will change Duration from 2 days to 4 days an I will get:

You may notice something that looks like a bug, but it is not! Duration * Units = Work. Duration = 4 days (e.g. 4 days * 8 hour per days = 32 hours). Units = 100%, work = 16 hours. So 32 hours (duration) * 100% = 16 hours! Is this a bug? NO! Microsoft Project 2010 keep the unit field the same, but calculates with Peak Field! Because I have fixed work (16 hours), and I put 4 days in duration field, the formula is Duration * Peak Units = Work.  4 days (4 days * 8 hours per day = 32 hours) * 50% (Peak Units) = 16 hours of work!

Why is that? Because when you change duration you do not want to change Units from 100% to 50% for other Task, but just for this particular one! And that is why in MS PROJECT 2010 introduce the Peak field.

Same thing will happens if I change Work from 16 hours to 32 hours in Task 3 (fixed Duration type):

Duration * Units = Work. Duration = 2 days (e.g. 2 days * 8 hour per days = 16 hours, and it is fixed). Units = 100%, Work = 32 hours. So 16 hours (duration) * 100% = 32 hours! Peak field is 200%! Because I have fixed Duration (2 days * 8 hours per day = 16 hours), and I put 32 hours in the Work field, the formula is Duration * Peak Units = Work. 2 days (2 days * 8 hours per day = 16 hours) * 200% (Peak Units) = 32 hours of work!

So don’t be confused it the Unit field remains the same. Always look at the Peak field!

Regards,