Today I learned that Excel incorrectly assumes 1900 was a leap year, and Microsoft will never fix it because the whole house of cards would collapse

Nestled away amongst a pile of recently updated pages on Microsoft's Learn site, which contains product documentation and technical resources, was a curiously titled article: "Excel incorrectly assumes that the year 1900 is a leap year." I thought that can't be right, surely everything would have fallen over long ago, but it turns out that this problem has long been known about among Excel-fanciers and Microsoft is never going to fix it: because then everything would collapse.

"When Lotus 1-2-3 was first released, the program assumed that the year 1900 was a leap year, even though it actually was not a leap year," reads the Microsoft explanation. "This made it easier for the program to handle leap years and caused no harm to almost all date calculations in Lotus 1-2-3."

Lotus 1-2-3 was the Excel before Excel, a hugely popular spreadsheet program by Lotus Software that helped IBM PCs break into and dominate the 1980s business market. There's no real consensus about whether this bug was a deliberate move on the part of Lotus' programmers to sa...