Year 1900 were not leap years, but Excel calculate with a leap year in 1900.
The date: February 29, 1900 should not exist, but it is it in Excel 2000,
2003 and 2007.
Excel makes errors in the date calculations involving the dates January 1,
1900 to March 1, 1900.
Excel calculate that the first of january, 1900 was a sunday, it was a
Quote from Wikipedia:
also evenly divisible by 400, in which case they are leap years. For
example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not."