Log in

No account? Create an account
entries friends calendar profile Previous Previous Next Next
12 hour clocks are wrong - Ed's journal
12 hour clocks are wrong
Something I was musing on the other day, was this:
Analogue, vs. digital.
Digital is all about breaking things down into slices. A digital readout will give you numeric representation of 'something'. An analogue one, is about a more holistic view - think about the fuel gague on your car - a easy display of 'full, getting low, empty'. If it's anything like mine, there's a way to see 'estimated miles left' but ... actually it's pretty hard to see how many litres are in your tank, mostly because it's just not very relevant. (Directly, anyway)

So anyway. Time then. I have a digital watch, because I like seeing the exact numbers for what time it is.
But I also have an analogue display on my phone, because I also quite appreciate the 'ish' sense of time.
But I do have my digital watch set to 24 hour format - I'd rather work that way, than have a time that requires an 'AM/PM' qualifier.

But through it all, I remain at a loss as to why we have 12 hour 'half days'. I mean, really. Why do we do this? I think 12 hours clocks are just ... fundamentally failing. If you look at a clock - on it's own - the information is incomplete. You need to add 'AM or PM' somehow. Maybe as simply as looking out the window, or just consulting your internal sense of 'is it morning', but ... still.

I do like the divisions of time though - 24 is a good number in that regard. Divisible by 1,2,3,4,6,8,12. That's very sensible. 60 minutes, similarly, divides well. OK, you can't really divide it by 8, but all the smaller sized slices it'll work with.
Look at the number of minutes in the day, and you'll actually see something which divides up very nicely by an awful lot of numbers. 1440 has 36 factors. You can integer divide it by every number between 1 and 10.

So the numbers are good.
But why do we _always_ divide the day by two? I mean, what's the point? Surely a far more natural 'analogue' readout of a day, is 24 hours? Midnight to midnight (or mid day to mid day if you prefer). One revolution per day.
That just makes far more sense, than an arbitrary division of a 'half day'. I mean, if you think about it, what does that 12 hours represent? Dividing it into 3 might make more sense - after all, you're liable to spend about 8 hours at work, 8 hours sleeping. But I still don't really see the point of dividing by two. Or at all.
24 hours, round the clock. With or without a minute hand, as you prefer. Visualise the hour hand as 'tracking' the sun, around the earth, and the progress of the day.

So I would like to suggest, that all you people with 12 hour clocks are wrong, and in error. Be they digital, or analogue alike.
Not least because the ante meridiem, post meridiem qualifier that you're using wrong as well. 3 AM - 3 hours ante meridiem is actually 3 hours before mid day.
And has built in confusion when you're talking about noon and midnight as well. In order to be entirely correct, you can't have 12:00 PM (or AM). You can sort of cheat, and look at 12:00:00.01 PM. But still.
12PM is always ambiguous. (12 hours post meridiem? Which day are are you referring to though).
Actually, technically speaking, midnight is _both_ 12PM and 12AM, where noon is neither.
But it doesn't get used that way, either.

So ... you see? We've got 12 hour clocks all around the world, 'because it's traditional' and for no other good reason.
And to refer you to a rather fabulous Demotivator: http://www.despair.com/tradition.html

Edit: And just before you ask - that analogue display on my phone _is_ 24 hours.
It's called Terratime and it's got a 24 hour readout, that also shows sun/moon rise and set, on that 24 hour display. It's a paid-for Android app, but I think it's well worth it, and not least because the developer was responsive to my feedback asking for a choice as to whether noon was at the top or the bottom of the clock, and to be able to turn off the minute hand.
It's also considerably cheaper than a Yes Watch

I've also found that Seldec Maritime do a selection of 24 hour clocks. Particularly one that has noon on top, which is a little more unusual. http://www.seldecpublishing.co.uk/clocks/
20 comments or Leave a comment
phlebas From: phlebas Date: January 10th, 2011 11:03 am (UTC) (Link)
Having an analogue clock go round twice a day rather than once does make a quick glance at the dial considerably more accurate, though.
sobrique From: sobrique Date: January 10th, 2011 12:02 pm (UTC) (Link)
Granted, that if you subdivide your analogue readout it becomes easier. I'm just not convinced that's anything other than arbitrary. I mean, we teach children how to read clocks at school. How much of that distorts readability?
phlebas From: phlebas Date: January 10th, 2011 12:10 pm (UTC) (Link)
I'm not convinced it's about education - an unmarked 24-hour dial would be very hard to read, whereas an unmarked 12-hour dial is fairly common and rarely causes problems (assuming you know which way up it goes). I'd imagine even with practice one-hour errors reading a 24-hour dial would outnumber 12-hour errors reading a 12-hour one by considerably more than 12 to 1.
sobrique From: sobrique Date: January 10th, 2011 12:43 pm (UTC) (Link)
Maybe not. But any subjective 'fairly common and rarely causes problems' is hard to really quantify, when we _do_ teach children that way, and they've had more exposure to a particular layout.

But talking about distinguishing a 15 degree angle, rather than a 30 degree angle. It's going to be harder, true. How much harder though? I'm not sure, and I'm not sure we'd be able to effectively tell, unless we lived in a world where people didn't get exposed to a 12 hours around the circle meme all over the place.
sobrique From: sobrique Date: January 10th, 2011 12:48 pm (UTC) (Link)
I guess the way you could check, is to see if you could reliably get 'half past the hour' from the hour hand alone. As that's the size of division we're talking about.
queex From: queex Date: January 10th, 2011 11:06 am (UTC) (Link)
I can't remember off the top of my head why the Babylonians split it neatly in two (assuming it was in fact them), but having seen 24-hour analogue clocks my impression was that they were annoying to read as the numbers were rather close together.

Also, 12-hour face means that the numbers are at intervals of 5 minutes, whereas under a 24-hour face they'd be at intervals of 2.5 minutes, making for a messier layout.

I think one aspect which traditionally always augmented the time shown on a clock was the amount of daylight; it's pretty easy to tell 6am from 6pm any time of the year. In the modern age of more window-less rooms and all-consuming artificial light, perhaps that cue is no longer as good.
mister_jack From: mister_jack Date: January 10th, 2011 12:24 pm (UTC) (Link)
The original hours divided the day into 12 equal segments and the night into 12 equal segments. The division into consistent hours is much more recent, following the development of mechanisms capable of reliably producing such time divisions (which is where the "O'Clock" comes from, it was initially a means of distinguishing the two systems).

I'm not sure how we ended up with 12 being noon. I'm guessing it's because it's the only well defined point in our timing system.
sobrique From: sobrique Date: January 10th, 2011 12:34 pm (UTC) (Link)
From what I can tell, noon was the 'fixed point' because you could reliably measure it, by length of shadow - shortest shadows = noon.
But then, the Romans counted down to noon, and counted up past it. And also they had 'daylight' as 12 hours, regardless of how long the actual day was.

I'm guessing that changed about when clockwork became possible - it's far easier to do 'count up twice'.
mister_jack From: mister_jack Date: January 10th, 2011 12:26 pm (UTC) (Link)
For watches, and clocks, it's pretty much irrelevant. If you really struggle to work out whether it's AM or PM then, frankly, your problem is bigger than watches!

A bigger problem is arranging times to do things, when the setup causes needless confusion.
sobrique From: sobrique Date: January 10th, 2011 01:00 pm (UTC) (Link)
I think the internet, and cross-timezone collaboration makes 24 hour format much more desirable.
Struggling to work out AM/PM? Well, yeah. Where I am, it's not too hard. Second guessing that guy I'm talking to across the internet, it's quite a bit harder.
cthulahoops From: cthulahoops Date: January 10th, 2011 03:39 pm (UTC) (Link)
My mental model of the day is very much divided into AM/PM. I think of lunchtime as 1 o'clock, work finishes at 6 or 7, and I'd expect to go to the cinema at 7 or 8.

Oddly, despite this I avoid 12 hour clocks. My phone is set 24 digital, every timestamp I see in work is 24 hour (or seconds since epoch) and my favourite watch ever was a 24 hour analogue.

It may be a stupid tradition, but for some reason my mind likes the extra work of adding and subtracting twelve all day.
queex From: queex Date: January 10th, 2011 05:09 pm (UTC) (Link)
I don't think it's correct to call it an issue of tradition- it's a standards issue.

As when considering replacing any standard, it's not just a case of saying 'this new version is better', you have to show that the benefit of adopting the new standard is worth however much mayhem there will be in the transition.

For how we measure time, I think that case for a change in standards is far from proven.
sobrique From: sobrique Date: January 11th, 2011 09:41 am (UTC) (Link)
Depends how much you like mayhem I guess? :).

Anyway, as for change in standards go - I think there's a firm case for using 24 hour notation, for written/digital times.

Avoidance of ambiguity.
Sorting when entered in on a computer. (Particularly if you embed the date as YYYYMMDD)
Ease of conversion in timezones.

I can't think where I last saw 'AM/PM' when typed, apart from for the sake of emphasis (.... and we were working until 3AM in the morning!). Does your experience differ on this?

24 hour analogue... well, would seem to logically follow from this. You're right, there would be a disruption. I think primarily you'd see it when time was being misread off an unknown clock somewhere - my 'hour hand' pointing at 10, would be the same as a 12 hour clock pointing at 11/23. Near enough that you wouldn't notice from your own internal time sense, but ... well, wrong.

But for personal timepieces, a non issue. You'd buy ... whatever you preferred. Clock on the railway, tend to be digital anyway.
queex From: queex Date: January 11th, 2011 11:08 am (UTC) (Link)
Oh, for written, definitely prefer 24 hour notation. Anyone who can't grasp the 24hr clock can't call themselves properly time-literate.

But then in conversation I'm much more likely to say '3' than '15'. And I don't think it's necessary to deprecate that terminology.

I think 24-hour analogue clock faces are pretty rubbish, though. Loss of precision, numbers on the half-tick and so on. Although I've never seen the particular attraction of analogue clock faces in general.
sobrique From: sobrique Date: January 11th, 2011 11:22 am (UTC) (Link)
I didn't used to like analogue readouts until I got a 24 hour one. I fell in love with the ones from 'yes watch'. Not least because they also included the ability to display the time digitally, and also marked on the dial things like sunrise and sunset.

But then, the analogue readout gave a very good indicator of progress through the day, and hours of sunlight. That, to my mind, is what analogue displays are good at, rather than precision readings.
It matters less that sunrise is at 16:16 today, than I have about 5 hours of daylight left, and a half moon will be in the sky, with lunar transit just as it's getting dark. (ok, it's 40%, and lunar transit is 17:23 but still, there'll be some moonlight, if it's not cloudy).
From: (Anonymous) Date: January 10th, 2011 07:09 pm (UTC) (Link)
Personally I use both, but for different purposes. Day to day for me I prefer analogue 12 hour as easier to read at a glance. I know whether it's morning, lunchtime or night so this is not an issue.

When sending details of time to meet people I prefer 24hr digital as less ambiguous, especially across time zones. But having spent a few years trying to teach people 24hr time I can assure you a lot of people do not find it easy. Visual thinkers prefer analogue anyway, and if you account for this with a 24hr analogue clock it gets a lot harder to read, especially if minutes are important. The people who don't like 24hr time are also likely to have more difficulty with things with a lot of numbers on.

So basically, it's a variant on what we inherited, but it works on a day to day basis so we keep using it. A pragmatic choice rather than a technical 'right' one.

sobrique From: sobrique Date: January 11th, 2011 09:57 am (UTC) (Link)
Thing is, how many people find '24 hour time' difficult, because they've been taught 12 hour time since an early age? I mean, I find a notion of time that doesn't have a 'reset' right in the middle of the day to be much more intuitive.

I think the reason it's 'difficult' is because they're thinking in terms of 12 hour time, and so converting back and forth. If you're looking at 19:00, and always converting that in your head, to '7:00, PM' then it is harder.
Your clock already has lots of numbers on it - there's 60 of them, around the dial. We deal with that little problem just fine though, by just making them really small, only displaying 'tick marks' or otherwise reducing how 'busy' the display is.

But I'll grant it's a convenience matter, and it's unlikely to change as a result.
dr_ogma From: dr_ogma Date: January 11th, 2011 08:50 am (UTC) (Link)
I disagree, I think that the 12 hour clock is fine.

I like the fact that the clock goes around about once while I'm awake.
I also agree with the point that a 24 hour analogue display would be busy, if not completely incomprehensible.
Given that the day divides into day and night, dividing the day into half days for the time seems to make a fair amount of logical sense.
sobrique From: sobrique Date: January 11th, 2011 10:11 am (UTC) (Link)
You lucky man. I don't get 12 hours sleep a day. I tend to work on about 8 (or less).
So I tend to see several of the hours twice in a 'waking' day, and ... a few that I won't see at all, in a 'working' day.
But then, I'm also awake in the night from time to time as well. Usually that's through partying, or late night gaming sessions, but occasionally it's because of work.

But still, it all feels pretty inconsistent to me.
I mean, you only get 'half day, half night' twice a year. And even then, it's from 0600-1800. You still end up with a mid day 'reset'.

Busyness - well, yes, it's harder to squeeze on 24 numbers than it is 12. But ... on the flip side, so is 60 numbers. We manage that reasonably well.
dr_ogma From: dr_ogma Date: January 11th, 2011 10:38 am (UTC) (Link)
I don't get 12 hours sleep either, the clock still goes round closer to once than twice. I think this comes back to Jack's point, "if you don't know whether it's AM or PM your problems bigger than watches." The hours I see twice a day with any regularity are 6-11, I'm constant enough with my sleep patterns to know which is which without any difficulty. I plan to keep it that way!
20 comments or Leave a comment