On Fri, 26 Feb 2010 11:58:32 -0800, "Joe User" <joeu2004 wrote:

Because WEEKDAY(A1,2) is 5, and 5 Jan 1900 was Thursday.

That's not quite the case. In point of fact, 5 Jan 1900 was a Friday :-))

But Excel thinks it was a Thursday!

This is one of the consequences of the Excel bug (which was said by some to
have been introduced in order to mimic a bug in the then dominant spreadsheet
program Lotus 1-2-3; although I suspect that may be just a CYA explanation)
which indicates falsely that 1900 was a leap year. So all the days prior to
Mar 1, 1900 are "off by one".
--ron