# 12:00 am/pm **URL:** \ **Category:** The BBQ Pit\ **Created:** [October 18, 2016, 6:55pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971 "2016-10-18T18:55:24Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![edwards\_beard](https://avatars.discourse-cdn.com/v4/letter/e/7bcc69/32.png) [@edwards\_beard](https://boards.straightdope.com/u/edwards_beard)\ **Post date:** [October 20, 2016, 12:46pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/21 "2016-10-20T12:46:05Z")
> [@SeaDragonTattoo](#): > > I work at a 24/7/365 facility. The clocks are AM/PM and they will stay that way because clients get confused, though some of the printed paperwork does show military time. **We also weigh everyone’s pets in kilograms.** I’m way too tired to be reading this…(bolding mine) I read this as “We also weigh everyone’s pets in Klingon” ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [October 20, 2016, 1:20pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/22 "2016-10-20T13:20:17Z")
> [@wolfpup](#): > > 12:00 PM is merely noon plus one of them dang arbitrarily small infinitesimals, which can be as small as you like right down to the Planck time and it’s still on the good side of “PM”. Or 12:00 AM could be noon minus one of them dang arbitrarily small infinitesimals. This isn’t a solution to the problem. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [October 20, 2016, 2:42pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/23 "2016-10-20T14:42:06Z")
> [@Telemark](#): > > Or 12:00 AM could be noon minus one of them dang arbitrarily small infinitesimals. This isn’t a solution to the problem. Since it’s ultimately arbitrary I was being only semi-serious. Still, I would argue that noon minus an infinitesimal is now 11:59:59.999999999… and not “12” any more. Since we agree that afternoon is “PM”, and 12:01 in the afternoon is therefore “PM”, so is 12:00 plus an arbitrarily small infinitesimal. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [October 20, 2016, 3:18pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/24 "2016-10-20T15:18:45Z")
> [@wolfpup](#): > > Since it’s ultimately arbitrary I was being only semi-serious. Still, I would argue that noon minus an infinitesimal is now 11:59:59.999999999… and not “12” any more. Since we agree that afternoon is “PM”, and 12:01 in the afternoon is therefore “PM”, so is 12:00 plus an arbitrarily small infinitesimal. As we’ve covered ad infinitum in another thread, 11:59:59.999… is exactly equal to 12:00 because infinitesimals really don’t work well outside of a very narrow range of operations. Either way, noon and midnight are precise definitions of the two times. Saying something is ante meridiem when it defines the meridiem seems imprecise. ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [October 20, 2016, 4:02pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/25 "2016-10-20T16:02:27Z")
> [@Telemark](#): > > Or 12:00 AM could be noon minus one of them dang arbitrarily small infinitesimals. This isn’t a solution to the problem. Except time is weird in that we tend to round it up, not down. If you want to make it in 5 seconds, 5.4 doesn’t cut it. It’s as if the mid point is moved back by .5 units. Not that that’s the answer. But it does involve infinitesimals. The real issue is that the point of noon or midnight is just that–a point. It’s infinitesimally small. For the vast majority\* of the time that the clock displays 12:00 AM, it is after midnight. The same is true if it’s 12:00:00 AM. Or even 12:00:00.00000 AM. \*Math term of art: almost surely. As in, there is a 1.000… chance that any randomly selected moment will be after midnight. There are an infinite number of moments after midnight, but only one moment that is not. Basically infinity minus 1 over infinity. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [October 20, 2016, 4:24pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/26 "2016-10-20T16:24:11Z")
What a cluster fuck of total ignorance … are you people _seriously_ confused about a.m. and p.m. … how the hell do you understand “Thursday”? For you high-and-mighty “I’m military grade” folks who use the 24 hour clock, is midnight 2400 or 0000? In case you’re clueless, the Earth completes one rotation in 23 hours 56 minutes. The Earth moves along it’s orbit in that time so it takes the extra four minutes for the sun to be in the same place in the sky. C’mon, man … measuring time in base-60 is soooooo 40th Century BC … I’ll not be able to find a citation for this, but I remember once reading the speculation that humans could not sit down a design a system of time keeping to be _more_ confusing that the one we actually use … I want to say this was in the remarks section of the PHP manual for the DATE ( ) function. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [October 20, 2016, 8:02pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/27 "2016-10-20T20:02:54Z")
> [@watchwolf49](#): > > For you high-and-mighty “I’m military grade” folks who use the 24 hour clock, is midnight 2400 or 0000? There is no 2400, by definition. It’s like saying 11:59 is followed by 11:60. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [October 20, 2016, 8:03pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/28 "2016-10-20T20:03:40Z")
> [@watchwolf49](#): > > What a cluster fuck of total ignorance … are you people _seriously_ confused about a.m. and p.m. … how the hell do you understand “Thursday”? For you high-and-mighty “I’m military grade” folks who use the 24 hour clock, is midnight 2400 or 0000? In case you’re clueless, the Earth completes one rotation in 23 hours 56 minutes. The Earth moves along it’s orbit in that time so it takes the extra four minutes for the sun to be in the same place in the sky. > > C’mon, man … measuring time in base-60 is soooooo 40th Century BC … > > I’ll not be able to find a citation for this, but I remember once reading the speculation that humans could not sit down a design a system of time keeping to be _more_ confusing that the one we actually use … I want to say this was in the remarks section of the PHP manual for the DATE ( ) function. Hey, while you’re berating everyone on their ignorance and imprecision, you may want to add in the 9.1704 seconds you left out in the sidereal orbital period of the Earth (AKA “the year”). [Seconds matter](https://en.wikipedia.org/wiki/Leap_second). ---
**Author:** ![I\_Love\_Me\_Vol.I](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/i_love_me_vol.i/32/521_2.png) [@I\_Love\_Me\_Vol.I](https://boards.straightdope.com/u/I_Love_Me_Vol.I)\ **Post date:** [October 20, 2016, 8:07pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/29 "2016-10-20T20:07:06Z")
> [@Morgyn](#): > > The military clock does prevent that confusion, but good luck getting anyone NOT in the military to use it. Most of Europe does, as well as the UK and many places in the rest of the world. Why is it such a problem for Americans? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 20, 2016, 8:30pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/30 "2016-10-20T20:30:35Z")
At any moment during daylight hours when the clock is displaying 12:00, it is PM, and at any moment during nighttime hours when the clock is displaying 12:00, it is AM. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [October 20, 2016, 8:39pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/31 "2016-10-20T20:39:32Z")
> [@gnoitall](#): > > Hey, while you’re berating everyone on their ignorance and imprecision, you may want to add in the 9.1704 seconds you left out in the sidereal orbital period of the Earth (AKA “the year”). [Seconds matter](https://en.wikipedia.org/wiki/Leap_second). All of life has done just fine these past 2.3 billions using simple binary: 0 = Night 1 = Day Seconds only matter when humans breed … ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [October 20, 2016, 8:43pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/32 "2016-10-20T20:43:17Z")
> [@Bryan\_Ekers](#): > > There is no 2400, by definition. It’s like saying 11:59 is followed by 11:60. Son of a gun! I actually didn’t know that! I thought 2400 was just another way of saying 0000. Hot dawg, I learned something from the internet! ---
**Author:** ![tonyfop](https://avatars.discourse-cdn.com/v4/letter/t/85f322/32.png) [@tonyfop](https://boards.straightdope.com/u/tonyfop)\ **Post date:** [October 20, 2016, 9:22pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/33 "2016-10-20T21:22:16Z")
> [@Bryan\_Ekers](#): > > There is no 2400, by definition. It’s like saying 11:59 is followed by 11:60. Funny thing, I am a military retiree, and I still work for the Navy, and our aviation management information system, called NALCOMIS, does not recognize 0000 or 2400. If an aircraft lands at midnight, it has to be logged as 2359 or 0001 because… because… Well because NALCOMIS is shit. ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [October 20, 2016, 9:39pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/34 "2016-10-20T21:39:41Z")
That’s the solution I fell back on, too, when I used to schedule appointments for a doctor who took his lunch break from 1:30 p.m. I scheduled people for 11:55 a.m. or 12:05 p.m. depending on various factors. 12:00 DID NOT exist. ---
**Author:** ![gigi](https://avatars.discourse-cdn.com/v4/letter/g/a587f6/32.png) [@gigi](https://boards.straightdope.com/u/gigi)\ **Post date:** [October 20, 2016, 10:12pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/35 "2016-10-20T22:12:22Z")
> [@SeaDragonTattoo](#): > > I work at a 24/7/365 facility. Speaking of which, that should really be 24/7/52 (or 24/365). Who’s with me?! ---
**Author:** ![Morgyn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/morgyn/32/3041_2.png) [@Morgyn](https://boards.straightdope.com/u/Morgyn)\ **Post date:** [October 20, 2016, 11:39pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/36 "2016-10-20T23:39:06Z")
> [@I\_Love\_Me\_Vol.I](#): > > Most of Europe does, as well as the UK and many places in the rest of the world. Why is it such a problem for Americans? Most of the rest of the world is also on the metric system, which Americans rejected as “too hard”. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [October 20, 2016, 11:52pm UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/37 "2016-10-20T23:52:17Z")
> [@Telemark](#): > > As we’ve covered ad infinitum in another thread, 11:59:59.999… is exactly equal to 12:00 because infinitesimals really don’t work well outside of a very narrow range of operations. Either way, noon and midnight are precise definitions of the two times. Saying something is ante meridiem when it defines the meridiem seems imprecise. To continue the world’s most pointless argument: Noon is the _ **transition point** _ between ante meridiem and post meridiem. Therefore noon-ε remains AM as ε tends to zero and will never take you over the transition for any finite value of ε, while noon+ε always remains PM as ε tends to zero. What happens precisely at zero is purely convention, but this supports the logic behind the convention wherein we routinely reset our timekeeping at the demarcation point. We see this at the transition point on the 24-hour clock where midnight is conventionally 00:00 and not 24:00, and by the same logic, the first instant of the start of a new day. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [October 21, 2016, 12:27am UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/38 "2016-10-21T00:27:13Z")
> [@wolfpup](#): > > To continue the world’s most pointless argument: Noon is the _ **transition point** _ between ante meridiem and post meridiem. Therefore noon-ε remains AM as ε tends to zero and will never take you over the transition for any finite value of ε, while noon+ε always remains PM as ε tends to zero. What happens precisely at zero is purely convention, but this supports the logic behind the convention wherein we routinely reset our timekeeping at the demarcation point. We see this at the transition point on the 24-hour clock where midnight is conventionally 00:00 and not 24:00, and by the same logic, the first instant of the start of a new day. If we started the day at 00:01, then the beginning of the first hour is 01:01, and the beginning of the second hour is 02:01 … this is the same problem we have by omitting the year 0 between 1 BC and 1 AD, the new century began on Jan. 1st, 2001 … bad enough we have to argue about this every hundred years, no way should we be allowed to argue the point _every day_ … because you know we would … ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [October 21, 2016, 12:45am UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/39 "2016-10-21T00:45:19Z")
> [@wolfpup](#): > > To continue the world’s most pointless argument: Noon is the _ **transition point** _ between ante meridiem and post meridiem. Therefore noon-ε remains AM as ε tends to zero and will never take you over the transition for any finite value of ε, while noon+ε always remains PM as ε tends to zero. What happens precisely at zero is purely convention, but this supports the logic behind the convention wherein we routinely reset our timekeeping at the demarcation point. We see this at the transition point on the 24-hour clock where midnight is conventionally 00:00 and not 24:00, and by the same logic, the first instant of the start of a new day. And, to use that terminology, my posts says that we always display time as x+ε, where x is the displayed measure of time. If a clock says it is 5:43 PM, it is actually indicating 5:43+ε PM. It will not indicate a time less than 5:43:00.000… PM. You can see this if you have a clock that lets you show or hide the seconds, like the one on most computers. If a clock shows 12:00, it will always\* be 12:00+ε. So 12:00 PM is afternoon, and 12:00 AM is after midnight. \*Almost surely, to use the math term. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [October 21, 2016, 12:55am UTC](https://boards.straightdope.com/t/12-00-am-pm/768971/40 "2016-10-21T00:55:30Z")
> [@Bryan\_Ekers](#): > > There is no 2400, by definition. It’s like saying 11:59 is followed by 11:60. I have seen 24:00 on train schedules and time tables in general before. It certainly is used. On a clock, though, you’ll always see 0:00. ETA: [Wikipedia actually has a sample image](https://en.wikipedia.org/wiki/24-hour_clock#/media/File:Railtime.jpg) of what I’m talking about. [Previous page](https://boards.straightdope.com/t/12-00-am-pm/768971.md?page=1) [Next page](https://boards.straightdope.com/t/12-00-am-pm/768971.md?page=3)