DATEDIF(), which means Date + Dif, is a compatibility function left over from Lotus 1-2-3 that Microsoft adopted in Excel version 2000, which is the only version that explains how this function works.

Excel’s SUM, DATE, WEEKDAY, IF, Nested IF, and IF/OR functions came to mind as I was watching a 1969 film called If It’s Tuesday, This Must Be Belgium, about American tourists on a whirlwind tour of ...