Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mailrus!ames!elroy!spacely!eto
From: eto@spacely.Jpl.Nasa.Gov (Edward Olsen)
Newsgroups: comp.sys.mac
Subject: EXCEL LOG10 Error on MAC II
Message-ID: <9367@elroy.Jpl.Nasa.Gov>
Date: 14 Sep 88 15:53:24 GMT
Sender: news@elroy.Jpl.Nasa.Gov
Reply-To: eto@spacely.Jpl.Nasa.Gov (Edward Olsen)
Organization: Image Analysis Systems Grp, JPL
Lines: 32
Keywords:Excel log10 math coprocessor

This is a repost.  I did not see it on comp.sys.mac the first time I
sent it and thus repost it.  Sorry if it made it the first time after all.


I have discovered what I classify as a bug in Microsoft Excel running on
a Mac II.  I am using Excel v1.5 and running sensitivity calculations in
dBm.  Thus I must take the natural logarithm of some very small numbers.

I find that if I take LOG10(2.7E-20) that I come up with a #NUM! error,
whereas LOG10(2.8E-20) computes fine.  The break point occurs at
			LOG10(2.7105054312138E-20)
If your number is a tiny bit smaller (change the 8 to a 7 just before the
exponent), #NUM! pops up.  Note that this is not a precision problem, for
I am not asking for a lot of significant digits.  I should be able to take
LOG10(1.0E-99) if I need to!  What is up here?  Of course, if you run this
test on a Mac Plus (no coproessor, just the SANE package) you do not get
#NUM!, just a bad precision number.  I called this in to the Microsoft
technical assistance and found it was an absolute surprise to them.

				 Ed Olsen



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