monline

The Excel in MS Office XP (aka. Office 2002) updated with SP3 does not handle leap years correctly. Follow my example to prove it.

The problem is that Excel considers the year 1900 to be a leap year, but it's not.

Try this:

1. Open a blank Excel document.
2. Enter the date 29th Feb 2000 (which was a real leap year) in the top-left cell.
   Take care that you enter the date in the short date format matching your regional settings. You can check this format mask in "Start Menu" / "Settings" / "Control Panel" / "Regional and Language Settings" / "Short date". If you enter the date correctly, then the cell contents will be aligned to the right. If Excel does not recognize the entered text as a date, then the cell contents will be aligned to the left.
3. Now enter 29th Feb 1900. The cell contents are aligned to the right, which means Excel accepted the value as a valid date.
4. You can go on and test with the years following (2100, 2200, 2300, 2400, ...). You'll see that later dates are handled correctly (which means that eg. 29th Feb 2100 is not accepted as a real date).

Btw. the definition of leap years: a year is a leap year (ie. February is 29 days long) if ...

1. the year can be devided by 4 AND cannot be devided by 100
2. or the year can be devided by 400