Calendars!

When working in finance, you care a lot about public holidays, because interest on wholesale loans between banks is calculated per business day. On global scale, there are more public holiday schemes than countries or timezones. And some countries change their public holidays willy-nilly on short notice.

Climate data lives in a wide variety of exciting calendars that no normal person would ever use. 360 day years? Check. No leap years? Check.

(I asked some of the scientists in my building, and apparently it makes the models a lot easier to write; just pushes the burden to post-processing)

Magnets