Excel incorrectly assumes that the year 1900 is a leap year (learn.microsoft.com)

by susam 32 comments 89 points
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32 comments

[−] nippoo 62d ago
In other "incorrect calendars" bugs, there's the Rockchip RK808 RTC, where the engineers thought that November had 31 days, needing a Linux kernel patch to this day that translates between Gregorian and Rockchip calendars (which are gradually diverging over time).

Also one of my favourite kernel patch messages: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin....

[−] tom_alexander 62d ago
My favorite: For one day all the Microsoft Zunes froze for the entire day, only to recover on their own 24 hours later when the infinite loop in their leap year code had finally resolved: https://web.archive.org/web/20090313105752/http://www.zunebo...
[−] gerdesj 62d ago
To be fair, that's nowhere near as daft as september, october, november, december. Latin for seven, eight, nine, and ten is: septem, octem, novem, decem. Those are the nineth, 10th, 11th and 12th months.

Edit: Whoops, correct eng -> latin nums

[−] emmelaich 62d ago
You may know this but originally they were 'correct' because the start of the year was March.
[−] teraflop 62d ago
Which wouldn't be that weird, except that the earliest Roman calendar started in March and ended in December, having only 10 months!

The Romans were of course well aware that this left a gap of about two months between the end of one year in December, and the beginning of the next year in March. But they just didn't bother counting this period as part of the calendar year. Presumably because there was no agricultural reason to need accurate dates during winter.

[−] _kst_ 62d ago
"I hate that SEPTember OCTOber NOVember and DECember aren't the7th, 8th, 9th, and 10th months."

"Whoever f---ed this up should be stabbed."

"I have excellent news for you."

[−] caminante 62d ago
No? How is it octem and not octo? Does the flat bar accent do something?

>The Latin word for "eight" is octō. [0]

[0] asked google

[−] scrlk 62d ago
An interesting read related to this bug from Joel Spolsky - My First BillG Review: https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...
[−] jdlyga 62d ago
Excel is so embedded into our world that we renamed part of the human genome to prevent excel from incorrectly reading them as dates

https://www.theverge.com/2020/8/6/21355674/human-genes-renam...

[−] eviks 62d ago

> If this behavior were to be corrected, many problems would arise, including: > Almost all dates in current Microsoft Excel worksheets and other documents would be decreased by one day.

Unless your fix adds a day to make them stay the same??

And these silly "compatibility" excuses are begins bugs affecting more and more unsuspecting users like that gene import conversion bug affecting a quarter of all published gene research papers.

[−] darknavi 62d ago

> Applies to: Microsoft Excel for Mac 2011, Excel for Microsoft 365 for Mac, Microsoft Office Excel 2003, Microsoft Office Excel 2007, Excel 2010, Excel 2013, Excel 2016

[−] Lammy 62d ago
I learned about this from my Macintosh back in The Day™, when a dead Parameter RAM battery would reset the system date to January 1st, 1904 at every boot:

- https://spinsidemacintosh.neocities.org/im202#im033-001

> “The date and time setting is also copied at system startup from the clock chip into its own low-memory location. It’s stored as a number of seconds since midnight, January 1, 1904, and is updated every second. The maximum value, $FFFFFFFF, corresponds to 6:28:15 AM, February 6, 2040; after that, it wraps around to midnight, January 1, 1904.”

- https://archive.org/details/mac_Macworld_Mac_Secrets_5th_Edi...

- http://preserve.mactech.com/articles/develop/issue_26/minow....

- https://preterhuman.net/macstuff/qa/ops/ops23.html

[−] jwrallie 62d ago
I was developing an interface to read a .xslx file to import a table within a Qt/C++ program, and this detailed showed up in my conversions to Unix time. It turns out Claude was amazing and brought up this issue as soon as Excel was mentioned, but terrible at actually fixing up the calculations.

I'd prefer using a .csv with dates already converted to Unix time, but no luck convincing the other people involved.

[−] antisol 61d ago
Aah, this old thing. Pops up every decade or so.

Reminds me of the good old "Falsehoods programmers believe about time": https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b...

[−] ComputerGuru 62d ago
This obligates me to share this absolute gem of date/time history folklore: https://neosmart.net/forums/threads/an-extended-history-of-t...
[−] shablulman 62d ago
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[−] stainlu 62d ago
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