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Ask HN: What does 12:00 AM mean?

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21–30 of 221 posts

Re: Ask HN: What does 12:00 AM mean?

#22
The way to remember this that finally clicked for me is that 'A' means 'ante', 'P' means 'post', and 'M' means Meridian some Latin word that means the sun is directly overhead. Or more practically speaking: noon.

12:00 PM is noon because one minute later, the sun is past being directly above. That is, it's 12:01 Post Meridiem. Since it would obviously be nonsensical for 12:00 AM to be immediately followed by 12:01 PM, noon is 12:00 PM by convention.

Extending this logic to midnight is left as an exercise to the reader.

Don't feel bad, I don't think anybody explained this to me until I was almost 30.

Re: Ask HN: What does 12:00 AM mean?

#23

Do you know what 12:01 AM means? 12:00 AM is one minute before that.

But you can also say: "Do you know what 11:59PM means? 12:00PM is one minute after that"

Midday and midnight are the points at which AM/PM change and you can't logically differentiate them by appending AM or PM. You just have to know the arbitrary cultural convention that midday is PM.

Re: Ask HN: What does 12:00 AM mean?

#27
For historical reasons[0], with 12-hour clocks, 12 is generally treated as zero. A general fix for this is probably something like Linux locale settings. It's going to be a rather flawed solution, what with those settings being super complicated.

[0]- Lore is that the sundial and dividing the day into 12 sections happened before the invention of the number zero, but I don't know if this is accurate.

Re: Ask HN: What does 12:00 AM mean?

#28
post #17

When working at international companies that have little interaction between countries (i.e. not so much that it would be standardized, but enough that it would be an issue): eventually everyone learns to write dates and times in both ways (14:00 / 2pm, 4/12 / 12 April). The Europeans think that they're translating for the "dumb Americans who can't count higher than 12", the Americans think they're translating for th…

> quirky Europeans who have to do everything special

so how many quarter inches are the footegg fields these days?

Re: Ask HN: What does 12:00 AM mean?

#29
> How do we solve this more universally?

Use this as an opportunity to realize that moving forward you need to be sure about times — especial for things that really matter. Using your European-ness and the fact that you’re an engineer isn’t an excuse. You can be disappointed in software and other people for the rest of your life and keep missing important appointments if that’s what you want.

Re: Ask HN: What does 12:00 AM mean?

#30
You have to learn other cultures' norms if you want to live or work with them. It goes both ways.

Europe and America do not only time differently, but phone numbers (1-800-123-1234 in the USA, 06 86 57 90 14 in France), dates (Jan 1 1911 would be 1/1/11 in the USA, 11-1-1 elsewhere), decimals (1,000.00 or 1.000,00), units (inches vs centimeters), reading order, daylight savings time, time zones (some countries don't even have them), etc. To say nothing of language and cultural differences, just formatting basic facts.

You don't solve it "universally", you make affordances for diversity the same way you allow for light/dark mode or language or any other user preference.

Not even all calendars have proper embedded time zone information so that's not always reliable either.

There is Unix time but you still have to convert that according to arbitrary rules, especially for countries that observe variable daylight savings like the US.

It gets even harder when you have to do math, like 00:00 Jan 1 1970 plus 30 years isn't automatically midnight of Jan 1 2000. It depends on whether you mean 30 * 365 24-hour days or some # of quartz vibrations or 30 * orbits around the sun or 30 * years of a certain country's time (adjusted for leap years and leap seconds and daylight savings and time zone changes mandated by new laws). There is no "right" answer. Libraries like Luxon or Momoent can help, but it's never easy.

That's just the reality of a multicultural business world. When in doubt, double check and reconfirm.

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