Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why is 11 am and 1 hour == 12:00 pm?

ell.stackexchange.com

Post reply on HN
Print view View original

11–20 of 67 posts

Re: Why is 11 am and 1 hour == 12:00 pm?

#11

Post by naikrovek »

FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

I believe the actual answer is that there is no 12:00 AM or PM. You're meant to say "twelve noon" or "twelve midnight" rather than AM or PM for this exact reason.

"actual answer" is maybe a bit strong - I read it somewhere but I can't remember where. The site or book or wherever it was that I read that did seem quite authoritative on the matter, however!

Re: Why is 11 am and 1 hour == 12:00 pm?

#12

Post by Symbiote »

ktpsns wrote: post #2

I don't want to be offensive, but this is just another example where anglo-american standards for time and length measurements are ill-defined and lead to confusion. Instead, we have the SI system for the rest of the world and we have international standards for counting time -- with time going from 00:00:00 to 24:59:59 a day. I wonder why people refrain to adopt a working system in favour of culture. I never underst…

> anglo-american

Do Spanish-American (and others) use kilos, metres, Celsius and all the rest? I'd assumed not, since the Quebecers I know use American measurements for their body and cooking. But I'd like to be wrong.

(You could also have meant anglophone, but that's too broad. 23:05 is fully understood in Britain, and the normal way to write the time on timetables and so on.)

Re: Why is 11 am and 1 hour == 12:00 pm?

#13

Post by ljm »

Finnucane wrote: post #7
FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric. And let's get rid of those pesky arbitrary time zones too. We should all be able to have our own personal time zones.

Measuring time over 24 hours rather than 12*2 hours makes it abundantly clear what part of the day you're referring to, no matter what timezone it is. It's not about putting everyone on the same time, but describing it without ambiguity.

This is especially important in language, where in some cultures the word 'tonight' actually translates to what you'd call 'last night' in English, for example.

Re: Why is 11 am and 1 hour == 12:00 pm?

#14

Post by deadbunny »

Finnucane wrote: post #7
FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric. And let's get rid of those pesky arbitrary time zones too. We should all be able to have our own personal time zones.

What? The 24hour clock has nothing to do with timezones. 11:00 is the same as 11am and 21:00 is the same as 9pm whatever your timezone.

Re: Why is 11 am and 1 hour == 12:00 pm?

#15

Post by coldtea »

Finnucane wrote: post #7
FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric. And let's get rid of those pesky arbitrary time zones too. We should all be able to have our own personal time zones.

>But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric.

Doesn't matter. Anything would be arbitrary. Just pick one and be done with it, and we already have GMT and UTC.

Re: Why is 11 am and 1 hour == 12:00 pm?

#16

Post by Fnoord »

Finnucane wrote: post #7
FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric. And let's get rid of those pesky arbitrary time zones too. We should all be able to have our own personal time zones.

> But whose 24 hour clock?

The one from your current timezone, obviously. And if you omit your timezone, you obviously mean your current timezone; the one you're residing in. If you're in Paris and you tell your kid dinner is at 6 PM then you mean local time. If your kid then comes home at 7 PM and says oh I thought you meant UK time then that's obviously your kid being a smartass. Even if you are both from UK. Why? Because it isn't practical to stick to a timezone you're not residing in.

Wether we're talking about 6 PM or 18 and 7 PM or 19 makes zero difference to your argument.

24H notation is just simpler and more practical. You don't have to resort to keyboard, it even takes up less space, and most importantly the context is less relevant ie. if AM/PM is omitted you still know what's up.

The only reason people stick to 24H notation, or imperial system for that matter, is "because we've always done it like this" ie. an argumentum ad antiquitatem. Not because it is better. Backwards compatibility comes with a price. You should always question whether the price is worth it.

I can think of one problem with the 24H system: analogue clocks like watches and churches. They use 12 hours. But when you watch that, that's communication to you as a human instead of human to human. And you know whether it is morning or evening, day or night, unless you're in a truly strange mental state.

Re: Why is 11 am and 1 hour == 12:00 pm?

#17

Post by mywittyname »

FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

Well, since 9.9999999... = 10 [0], then 50 + 9.999999... = 50 + 10

Given that, to you claim, 11:59.59.99999[...] is still AM, then 11:59:60 is still AM, thus 12:00:00 is still AM.

[0] https://www.youtube.com/watch?v=SDtFBSjNmm0

/s

Re: Why is 11 am and 1 hour == 12:00 pm?

#18

Post by 21 »

naikrovek wrote: post #11
FabHK wrote: post #5

I thought continuity provides an answer: 11:59:59.9999999999 is still AM. 12:00:00.0000000001 is clearly PM. When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm. Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock. That also removes the ambiguity whether "Midnight on J…

I believe the actual answer is that there is no 12:00 AM or PM. You're meant to say "twelve noon" or "twelve midnight" rather than AM or PM for this exact reason. "actual answer" is maybe a bit strong - I read it somewhere but I can't remember where. The site or book or wherever it was that I read that did seem quite authoritative on the matter, however!

Right. And what should I do if I'm a digital clock with limited space?

Re: Why is 11 am and 1 hour == 12:00 pm?

#19

Post by mc32 »

makecheck wrote: post #8

You’ll probably never see a flight or a movie or something start right at 12:00; it’s just so much clearer at a glance to see that 11:55 AM/PM.

But special sales at stores and online do begin at midnight. Say new playstation, iPhone, Xbox, etc.

Re: Why is 11 am and 1 hour == 12:00 pm?

#20

Post by naikrovek »

21 wrote: post #18
naikrovek wrote: post #11

Earlier quoted context omitted.

I believe the actual answer is that there is no 12:00 AM or PM. You're meant to say "twelve noon" or "twelve midnight" rather than AM or PM for this exact reason. "actual answer" is maybe a bit strong - I read it somewhere but I can't remember where. The site or book or wherever it was that I read that did seem quite authoritative on the matter, however!

Right. And what should I do if I'm a digital clock with limited space?

I imagine you're not pondering this problem if you're a clock.
Post reply on HN