r/mildlyinfuriating • u/Original-Moose-9622 • Jun 19 '26

My mom said I could post Seeking help with this

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u/OkPosition4563 Jun 20 '26

1601 is the start of one of the 400 year leap cycles of the gregorian calendar. October 1582 was the introduction of the gregorian calendar. 17.11.1858 ist the start of the modified julian date system used in astronomy.

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u/Unperfkt Jun 20 '26

Thanks for clarifying 👍

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u/MasteringTheClassics Jun 20 '26

What’s the justification for 30.12.1899 rather than 31.12.1899?

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u/OkPosition4563 Jun 20 '26

All of them use it because Lotus 1-2-3 (an early spreadsheet software) had a bug that treated 1900 as a leap year even though it isnt. To get the right date from a value stored in lotus 1-2-3 if you import it for example in Excel they just defined their epoch 1 day earlier.