1900 was not a leap year, despite what Excel might have you think

If you enter 29 February 1900 into Excel, it will recognise it as a date and format it such. But if you can find a calendar dating back that far, you'll discover that 1900 was not a leap year.

This bug was purposely introduced by Excel to keep it in step with other systems that had been created before Excel's inception. In all but very exceptional circumstances, no one will notice.

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