For what it is worth:
I am convinced it is due rounding. If in the cell where you have
"=39.83*65 gives 2588.95" you modify the equation slightly
and make it =(39 + 50/60)*65 you then get the 2589.17 that
you were expecting.
Just my 2 cents worth.
Joe
Ross Johnson wrote:
Richard
Detwiler wrote:
Bob Long wrote:
"Matt Wlazlo" <[EMAIL PROTECTED]>
wrote in message
news:[EMAIL PROTECTED]...
On 6/3/06, Bob Long
<[EMAIL PROTECTED]> wrote:
I'm noticing some strange
behavior while calculating prices on my invoice.
A1=39:50 (hours worked)
A2=A1*24 (==39.83)
A3=65 (rate)
A4=A3*A2
Now A4 will equal 2589.17. But, somewhere else in the spreadsheet,
typing =39.83*65 gives 2588.95!
I think you'll find it is a
rounding issue. If you change the format of A2
so that you see more decimals, you'll see that it is really 39.833333
(recurring, I presume). Multiply *that* by 65 and you'll get 2589.17.
I tried re-adjusting the formatting of A2, but to no avail.
More specifically, what did you do? Did you change it so you see more
decimal points? You should be able to see 39.833333... rather than just
39.830000.
I changed the number of decimal points. The cell reads 39.833333333...
Strangely, if I manually calculate
=39.83*65, it correctly gives
3588.95. Even windows calculator gives the same result. So I don't
think it's a fp precision problem.
It's not a precision thing. Calc is holding the correct value
internally.
It's just that 39.833333... is not the same number as 38.830000!
Ahh! Finally got it. I used ROUND(A2;2)*65 to get the correct answer.
Which just begs the question of what is *really* correct! 39:50 (hh:mm)
is 39.833333... (recurring). 39:50 is *not* 39.8300. So if you are
rounding to lose some digits, you *may* be propogating errors in
subsequent calculations. It really depends on how you are defining
things for your purpose; just be careful, is all I'm saying.
I agree with Bob. Rounding does NOT give you the "correct" answer. The
correct answer is the one you had in the first place, even though it
didn't seem correct on the surface, because if you used 38.8300000 in
the calculation, you'd get a different answer. But the one you got in
the first place was "correct", and the one you got when you used
38.8300000 was "incorrect". So I'm not sure why you're introducing the
ROUND function to knowingly give you an incorrect answer.
In any case, the difference between rounded and not rounded is about
0.008% -- in my opinion hardly enough to worry about. But you did have
a concern that you had this tiny difference, in which case, I'm again
not sure why you would ROUND to give you an answer which is incorrect.
It all depends on what is actually shown on the invoice - 39:50 or
39.83. Usually it's the hr/min, so rounding would be incorrect. And it
may only be a small difference, but someone else may be checking the
figures, and you don't want them coming up with different answers and
then doubting every other calculation you do.
Ross
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