Excel 2007 has different ways of guessing whether a difference is zero.
It's one of its known problems, and you'll see frequent reports in the
archives of this and other excel newsgroups.
--
David Biddulph

"Gee" wrote in message
...
OK, all that said and my subsequent confusion, I never had a problem with
this kind of thing in '03, only in '07 and I'm still working on another
problem with it but the 13 decimal places solved the Yes/No problem just
fine.
Thanks so much for your help.

....

"JoeU2004" wrote:
....
But using ROUND in comparisons with numbers with decimal fractions is
okay,
when done correctly. For example:

=if(and(400.5<=round(HI2,1),round(HI2,1)<402.5), "YES", "NO")

This is okay because ROUND ensures that the internal binary
representation
of its result exactly matches a constant with the same number of decimal
places. For example, if A1 is =10.1-10, =(A1=0.1) returns FALSE, but
=(round(A1,1)=0.1) returns TRUE. The reason is: the binary
representation
of 10.1-10 is not close enough to the binary representation of the
constant
0.1 for Excel to consider them equal.

In contrast, if A1 is =0.1+2^-56, =(A1=0.1) returns TRUE even though the
binary representations of A1 and 0.1 are not the same. Likewise, =A1-0.1
returns zero. But =(A1-0.1) returns non-zero, namely about 1.39E-17.
And
=IF(A1-0.1=0,TRUE) returns FALSE, which flies in the face of reason
considering the result of =A1-0.1, until we understand Excel's dubious
heuristic for determining "close enough".
....