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From: John on 12 Mar 2005 13:17
People,
Last week a poster asked for a method of finding the number of elapsed
days between two dates in Project. I, being bold and brave, answered
with a simple formula that could be used with a customized duration
field. The formula was:
Duration1 = DateDiff("d",[Start],[Finish])*480
The factor of "480" is needed to re-convert the format when using a
spare duration field.

I tested the formula on a sample file and "boom", problem solved.
Well... not quite. A fellow MVP (Gerard Ducouret) countered with the
fact that an extra day needed to be added to the formula to make it
work. The "fudge" factor in Gerard's modification to my basic formula
was needed but neither of us knew why. After a few off-line e-mails
between us, I realized, I CAN'T COUNT.

After some head scratching I finally found the switch so the bulb could
be turned on. Now I "see da light!"! The following is an excerpt of what
found and wrote to Gerard.

"First, I apologize, when I said my formula worked fine, I wasn't
counting correctly. I was so focused on a 7 day week that I counted one
Wednesday to the next as 7 days. Wrong! It's 8 days. Wednesday morning
to the next Tuesday evening is 7 days. It is so easy to assume what we
think we know. Bad.

Ok, now that my embarrassing confession is out here is what else I
realized. Since we work with Project so much, we (or should I say "I")
tend to think in terms of working days even if our mouth is uttering
elapsed days. For example, the span between Monday at 8:00 am and Friday
at 5:00 pm is not 5 days as we so quickly surmise. It is in fact 4 days
of elapsed time. Monday 8:00 am to Saturday 8:00 am IS 5 days. Remember
- elapsed time works in 24 hour days. So in effect, the fudge factor I
accused you of using indiscriminately is probably needed to translate
what our minds can't see. Although, now that I have "seen the light", a
much better approach to elapsed time would be to use "hours" instead of
days and then convert to days."

Being an MVP doesn't mean I won't screw up once in a while. I also
apologize to the original poster for a bad formula. Hopefully the above
explanation clears up the matter.

John
embarrassed MVP
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