The story goes that since Lotus 123 was the dominant spreadsheet program when
Excel was being developed and since Lotus 123 thought that 1900 was a leap year,
that MS had a choice--do it correctly or do it to match Lotus 123.

By matching Lotus 123's mistake, it would be easier for users to migrate from
123 to Excel.

And since every company wants users and wants to make that transition as easy as
possible, the decision was probably very easy to make.

Lex_Muga wrote:

Why is MSExcel accepting the string `2/29/1900' as a legal date?
In fact it also determines '2/29/1900' as a WEDNESDAY. 1900 is not a leap
year since it is divisible by 100 and not divisible by 400.

January 1, 1900 is marked as Sunday by MSExcel. According to
Perpetual Calendar available on the web, it is a Monday.

The corresponding weekday for each date from Jan 1, 1900 to
Feb. 28, 1900 is not correct. The weekdays from March 1, 1900
onwards are correct.

However, the serial numbers starting from March 1, 1900
are wrong. This is the reason why when I computed for the number
of days from Jan 1, 1900 I always get a result that is higher by 1
from the correct figure.

--
Felix Muga II
Mathematics Department
Ateneo de Mania University
Philippines

--

Dave Peterson