Talk:12-hour clock
11:59 am = midnight???
- Traffic regulations in San Francisco use 11:59 am and 11:59 pm, for midnight and noon respectively.
This statement appears to be incorrect (at best, midnight and noon are reversed), and since I don't know where to check the facts I have just deleted it. Ray Spalding 22:11, 1 Jan 2005 (UTC)
San Francisco isn't the only place that does this. According to NIST, train and plane schedules in the US do a similar thing. (Only correctly, of course.) -- Toby Bartels 00:12, 4 Jan 2005 (UTC)
- A perhaps more accurate description than "11:59 am = midnight in San Francisco and elsewhere" would be to say that these places never schedule any event exactly at midnight or noon, because they lack a convenient notation for these two points in time. Markus Kuhn 15:52, 1 January 2007 (UTC)
- I looked up the SF traffic code, the only reference to 11:59 is midnight, which is covered in the article and not unique to san francisco. No mention of any 11:59 of either kind for noon (well, if the quote were correct, this 11:59 pm could conceivably mean noon, except that'd be a funny time for new meter regulations to take effect.) --Random832(tc) 13:42, 31 January 2007 (UTC)
Reason for 12-hour increments
Why did the Sumerians or Egyptians use 12 hour increments? Did this concept of "12" derive from the number of notes in the chromatic musical scale? Or perhaps it has some religious significance relating to astrology? -- 216.102.9.150.
- The article that I linked above is unclear; but I don't think that the chromatic scale is anywhere near that old. -- Toby Bartels 22:34, 5 Jan 2005 (UTC)
The Sumerians had a base-60 numbering system. So that explains why there are 60 seconds in an hour and 60 minutes in an hour.. Now look at degrees, notice how 40°12'13" is 40 degrees, 12 minutes, 13 seconds... There are 360 degrees in a full orbit, or 6060. But having 180 hours in the day (3060), well that's excessive. Let's try dividing by 15, we get 12... Why 15? well 60 can be factored these primes 2,3,5 any multiple of them makes a nice simple divisor, so 2,3,5,6,10,12,15,18,30 are your basic options, of those the only ones that make sense here are 18, 15, 12, 10. Why they chose 15 not 12 or 18 I can't tell you, maybe they just thought 15 or 18 hours were still excessive, and 10 too few? Maybe 12 was better because it could be divided twice in half? --Zenyu 21:55, Jan 5, 2005 (UTC)
The used base 60 system not a 180. 12 is 60/5 not 15. 68.239.208.239 19:58, 7 May 2006 (UTC)
I'm new to wikipedia, so I don't know if this edit is appropriate, so forgive me if it's not. I would like to know why the 12 hour increments instead of 10. If the reason is that the Sumerians had a base 60 numbering system, thats great, but raises the question why a base 60 and not 10? Surely with 10 fingers its a more obvious choice? — Preceding unsigned comment added by 195.248.96.13 (talk • contribs)
- 12 hours for daytime and 12 hours for nightime come from the Eqyptians who divided the night and day in that manner. The reason for a base 60 numbering system in Sumeria/Babylonia is unknown, but it was actually a base 6×10 numbering system, so there was a kind of base 10 system within it (see Babylonian numerals). Sumeria/Babylonia never used a 24-hour day or a 12+12 hour day. Instead their day had 12 double hours (each called a beru), similar to the 12 double hours in China. But the basic time unit in Babylonia was not the double hour — it was the time-degree (called an us), the time it takes for the celestial sphere to rotate one degree (1/360th of a rotation) around a motionless Earth (4 minutes), so a beru had 30 us. — Joe Kress 04:02, 13 December 2006 (UTC)
Meaning of 12:00 am/pm
Noon is 12:00 PM, and Midnight is 12:00 AM. This is subject to debate? Theanthrope 17:00 6 Jun 2003 (UTC)
That's my thought exactly. Although it is rather odd that AM and PM change at 12 instead of 1, I've never ever run into a situation where the two were confused. Still, I tend to abbreviate them as 12m instead of 12a, and 12n instead of 12p, just for accuracy. --rj 5:46 12 Aug 2003 (UTC)
A digital clock will display "12:00 AM" for midnight, and "12:00 PM" for noon. This is probably because it makes the engineer's job easier, as "12:00 AM" (midnight) is one minute before "12:01 AM", and "12:00 PM" (noon) is one minute before "12:01 PM". Any other convention would require more work for the engineer making the clock. --Juuitchan
Apologies for dredging up an old issue here, but I wonder if this is a European vs North American difference? When growing up (in Britain) I was taught that noon and midnight were neither AM or PM, and that to write 12AM or 12PM was ambiguous nonsense. Only when I moved across the Atlantic did I realise they were commonplace. In fact, my first encounter with them was in a small town in upstate NY, where a roadside sign read "No Parking 12am to 12pm" - I couldn't interpret it, and had to go and park elsewhere! Does anyone know different? If not, I'll put a remark to this effect in the article. Cambyses 16:48, 27 May 2004 (UTC)
- It would be nice to have in the article a photo of such a "No Parking 12am to 12pm" sign! Markus Kuhn 17:44, 8 April 2006 (UTC)
But the US standards body NIST agrees with the allegedly European convention: noon is neither AM nor PM, while midnight is both. I suspect that the real disconnect is official standard vs common practice, rather than Europe vs North America -- but the common practice is more common in North America. I will explain the NIST standard in the article. -- Toby Bartels 00:12, 4 Jan 2005 (UTC)
Noon is not 12:00 PM. "Noon" is an exact reference point in time - the meridiem itself. 12:00:00 PM is the one-second interval immediately following the meridiem; 12:00 PM is the one-minute interval immediately following the meridiem. Digital clocks indicate the current time interval; they (correctly) read 12:00 PM for the one-minute interval immediately following noon. At noon, no matter how finely measured, a (12 hour) digital clock should be busy changing its display from "11:59 AM" to "12:00 PM." The confusion over "noon", "midnight", "12:00 AM," and "12:00 PM" vanishes when the convention of differentiation between a point in time and a time interval is adopted. -- Scott Wagner 19:17, 4 Jan 2005 (UTC)
What do you mean "noon is ... the meridiem itself"? You must have meant that noon is when the sun crosses the meridiem. But that is incorrect because of the equation of time (true sun vs. mean sun), time zones, and daylight saving time. See my entry below for more detail. --Alan E. Feldman 2005-12-04 18:32 UTC.
I don't think that it's as simple as saying that "12:00" means an interval, not an instant. The same notation is used for both. Nevertheless, you're quite right that when a digital clock says "12:00", then it means an interval. So I guess that there is no conflict between the time display and the NIST standard that noon (an instant) is not PM. However, when you set your alarm for noon, then I claim that there is a conflict! -- Toby Bartels 22:34, 5 Jan 2005 (UTC)
The first two paragraphs of section "Ambiguity at noon and midnight" are incorrect. I quote them below and comment:
[begin quote] According to the actual meaning of the terms ante meridiem ( a.m.) and post meridiem ( p.m.), as well as standards bodies such as the National Institute of Standards and Technology in the United States, noon (which falls precisely at the meridiem or celestial meridian) is neither a.m. nor p.m., because noon is neither before nor after itself. [end quote]
What does "noon which falls precisely at the meridiem or celestial meridian" mean? Noon doesn't fall anywhere. OK, this was really meant to say that the sun is on the celestial meridian at noon, but that too is incorrect! First of all there is local sun time vs. standard time. The sun *does* cross the celestial meridian at 12:00 local solar time, but we don't go by local solar time -- we go by standard time. The actual position of the sun in the sky determines local solar time. But standard time differs from local solar time in two ways: 1.) Local solar time goes by the position of the true sun while standard time goes by the mean sun (which gives us mean solar time) as determined by atomic clocks. 2.) Local solar time varies with longitude while standard time varies with time zone.
The difference bewteen local solar time and mean solar time is caused by the non-uniform "motion" of the sun acorss the sky. This non-uniform "motion" is caused by the tilt of the earth's axis with respect to its orbit and by the fact that the speed of the earth in its orbit around the sun is not constant but varies according to Kepler's Second Law. The difference between local solar time and mean solar time is given by the equation of time. The result is that the sun is as much as about 15 min. slow or fast compared to mean solar time, depending on the time of year.
So, while the sun *does* cross the celestial meridian at 12:00 local solar time, it almost never does so at 12:00 standard time.
Here's an example: Assume it's late October and you live at 75 deg. longitude. The equation of time then gives the sun as being approx. 16 minutes fast. So, using the strict interpretation of the original definitions of AM and PM and the article's definition of "noon" we would get the following times:
11:42 am 11:43 am 11:44 noon (= 12:00 local solar time which is when the sun crosses the celestial meridan) 11:45 pm 11:46 pm ... 11:59 pm 12:00 pm 12:01 pm 12:02 pm
And the crossover point -- "noon" according to local solar time -- would vary throughout the year! The crossover point would also change by 4 min. for each degree of longitude the observer is from his time zone's central meridian. This shows the fallacy of slavish adherence to the old, obsolete, archaic definitions of AM and PM. Current usage is clearly not according to the original definitions! This is because the original definitions refer to local solar time while in the modern era we instead go by standard time. (And I haven't even touched on daylight time!)
[beg quote] Despite this definitive logic... [end quote]
Well, I have shown about that this is not "definitive logic". The original definitons for AM and PM came into being in the 1600's or so (reference forthcoming) when people went by local solar time. It made perfect sense for that. But obviously we have come a long way when it comes to timekeeping. We have smoothed out the non-uniform apparent motion of the sun across the sky using atomic clocks. We have set up time zones to simplify (civil) time's dependence on longitude and daylight saving time to save daylight. The result is that the sun almost never crosses the celestial meridian at noon (civil time) and therefore it is high time to replace the archaic definitions with the modern de facto convention, namely, that midnight (00:00) is 12:00 AM and noon (12:00) is 12:00 PM in the 12-hour AM/PM system. This convention is so simple, so logical, so natural, so sensible, and so mathematical that it practically forces itself upon us. And in fact it aleady has. Note that digital clocks in practically all devices use this convention which has made it the de facto convention. (This is assuming that the clock uses am and pm to distinguish between noon and midnight. I have seen 12:00 M for midnight and 12:00 N for noon on Cable TV on-screen TV schedules. Not that there's anything wrong with that!)
It is the best and the de facto convention because it allows us to treat the am/pm value as just another column in the date-time construct (which, of course, simplifies programming). By considering pm to be greater in value than am (you could do this by using am=0 and pm=1) you simply use the normal rollover rules. Yes, am/pm times are typically written with am/pm out of order, but we already have the components of the date in different orders that vary by country yet they still follow normal rollover rules. In natural order we get
yyyy-mmm-dd am/pm hh:mm:ss.cc
It's very simple if you also assume 12 in the 'hh' column to be equivalent to zero. When hh=11 rolls over to 12 (effectively 0), the am/pm value is incremented. When pm (1) rolls over to am (0), the day is incremented. Etc.
So since the original definitions of am and pm apply to local solar time, and since we live by civil time to which the de facto convention outlined above applies, the "ambiguity section" in the article needs to be rewritten. And while the 24-hour format avoids this problem altogether, if one is goint to use am/pm, this is the way to do it.
I acknowledge that NIST and other similar bodies insist that noon and midnight are neither am nor pm, but I believe they should rethink this issue and their position only continues to cloud the issue. They don't even mention the de facto convention which is needed for people who look up this FAQ question to determine how to use and interpret 12:00 AM and 12:00 PM (which is needed for using digital alarm clocks, VCR's, personal computers, etc.) They could at least do that!
They could say that while technically, according to the original definitions of ante meridiem and post meridiem, noon and midnight don't fall into either class, the modern world runs on the new de facto convention (12:00AM = midnight, 12:00PM = noon). They could even explain the difference between local solar time and civil time and such. And they could still mention the use of "tricks" like 12:01, etc., to avoid possible confusion.
If all this *still* doesn't convince you, consider AD and BC. Imagine the same slavish adherence to the original definitions of these terms. The calendar as we know it would completely fall apart. Why? Because we don't know for sure just what year Christ was born. Scholars almost universally agree that Christ was born during the BC period, probably between 7 B.C. and 2 B.C. So to be strictly correct, we'd have to re-number all our years! But it's even worse. Since we don't know the exact year, we wouldn't know HOW to re-number the years. And we probably wouldn't re-number the years *even* if we *did* know: Imagine the confusion that would result!!! Therefore, we have done the sensible thing: We use the de facto definitions of AD and BC which are such as to simply keep the current numbering of years unchanged. --Alan E. Feldman 2005-12-04 20:03 UTC. (Minor correction at 2005-12-04 22:17 UTC)
- The long story above just shows that am and pm have no hard relationship to the apparent position of the sun. This is not only true for noon and midnight, but depending on time zone and season the difference between solar time and clock time can easily deviate for more than an hour. During daylight saving time 12:30 pm is almost surely before solar noon (before the sun passes the meridian). So the discussion on the precise meaning of 12:00 am/pm has nothing to do with the position of the sun. It looks to me like the theoretical meaning can only be wether the time is before or after noon. So the discussion in the article stating that 12:00 is neither am nor pm is wholly correct. Of course this does not deny that the most logical extension of the meaning is for 12:00 pm to be shortly before 12:01 pm, as is the usual designation on digital clocks. But even this is only marginally logical since 11:59 pm is then not shortly before 12:00 pm. −Woodstone 19:24, 4 December 2005 (UTC)
The article is not wholly correct:
[begin quote] According to the actual meaning of the terms ante meridiem ( a.m.) and post meridiem ( p.m.), as well as standards bodies such as the National Institute of Standards and Technology in the United States, noon (which falls precisely at the meridiem or celestial meridian) is neither a.m. nor p.m., because noon is neither before nor after itself. [end quote]
Contrary to the above quote from the article, noon (civil time) does not fall precisely at the meridiem. Noon is a time, not something that can be on the meridiem. Even with the obvious correction, "noon is when the sun 'falls' on the meridiem", it is still wrong as I demonstrated above. Therefore, the article is not wholly correct. If anyone needs to know how noon and midnight are classified w.r.t. am and pm, they are almost certainly asking about civil time for which there is a clear, sensible, logical, and mathematical de facto convention. The original definitions, which apply only to local solar time (which almost no one uses today) are irrelevant in our modern world. Given the am/pm system as it is, the de facto convention is correct for civil timekeeping in the modern world. Denying noon and midnight am/pm assignments does no good and in fact causes further confusion; it is unfortunate that NIST and other time authorities refuse to recognize this. And finally, if you interpret 12 as zero, 11:59 pm being followed by 12:00 am is totally logical. It's certainly no less logical than January, February, ....
--Alan E. Feldman 2005-12-04 22:17 UTC.
Oops. Meridiem means middle of the day. So noon falling on that makes sense. But the article equates that with celstial meridian, so it's still wrong! And now we get into what "middle of day" means. OK, if middle of day means 12:00 civil time, then yes, strict application of the old definitions gives noon and midnight no am or pm designation. But the de facto convention still exists and is the most useful answer to the question. If you discover a file on your computer and it is labeled 12:00 am, you need to know the de facto convention to know if the file's time stamp is noon or midnight. So we may as well redefine am and pm to be what they already are in the modern world. am covers the interval [00:00,12:00) and pm covers the interval [12:00 24:00) using parenthesis to indicate open ended (exclusive of the end point) and brackets to indicate closed (inclusive of the end point). And the times are given in 24-hour format. --Alan E. Feldman 2005-12-05 06:22 UTC.
Well, the new write-up is better, but it still worships the old definitions too much. The article says that "despite this strict logic" resulting in no am/pm assignments for noon and midnight, it is "common practice" to have noon as 12pm and midnight as 12am. It is more than common practice: it is the de facto convention, confusing or otherwise.
Do we stick with the original definitions (or usage) of will and shall? NO. These words have evolved. Why can't am and pm evolve? What is so terrible about a new definition? If people who wrote articles about am and pm clearly described the new de facto convention and why it came about and how logical and mathematical and sensible it is, there would be LESS confusion. It would be a reference. In English, spelling is confusing. But we don't re-spell everything phonetically to avoid confusion, do we? People have to learn the words. And if a writer is unsure of a spelling, he or she can look it up in a dictionary! The same should be for am and pm. The American Heritage Dictionary, to its great credit, says the following:
Usage Note: By definition, 12 A.M. denotes midnight, and 12 P.M. denotes noon, but there is sufficient confusion over these uses to make it advisable to use 12 noon and 12 midnight where clarity is required. (see <http://dictionary.reference.com/search?q=AM>)
That's the right way to do it!
Then there is the part talking about the "technical inaccuracy" of the de facto convention. I ask this: How do we really know that the people in the 1600's didn't happen to use the de facto convention? Does it even matter? They used local solar time. We're pretty sure about that. But in today's modern world we use UTC and standard time. Why is standard time okay but not the new de facto am/pm convention? They may or may not have assigned 12pm to noon and 12am to midnight. Why does it matter? In any instance where the time is given as 12:00 AM or 12:00 PM you need to know what it means. Back then, if someone asked you the time, they expected to get the local solar time. Do that today and you're likely to miss the plane! So "What time is it?" has evolved from local solar time to standard time (which is based on UTC, of course). And am and pm have also evolved.
In today's world, 12 AM is midnight at the beginning of the day and 12 PM is noon, period. Why do so many worry about adapting AM and PM to our modern world? Do we do this with ANYTHING else? Words evolve. Timekeeping evolves. The second used to be 1/86400th of Jan 1 in 1900 or 1940 or something like that. Now it is a certain number of oscillations of a certain atomic process. The meter has gone through SEVERAL re-definitions. If we are going to stick with c. 1600 definitions, shouldn't we go back to local solar time? I mean that's what was used when am and pm came into being. And why is no one similarly fussy about using "strict logic" to interpret AD and BC? No one says that our current usage of AD and BC is "not strictly correct" or "technically inaccurate". Moreover, application of "meridiem" is "technically inaccurate" because it assumes local solar time, which is not in general use today.
If one wants to use, or suggest to use, tricks like 12:01 and 11:59, etc. in written schedules, notices, and similar, be my guest. There's nothing wrong with that. But I think the article should be a little more accepting of the new de facto convention and give better reasons for it: namely, that in the case where one is restricted to using am and pm to distinguish noon from midnight, it is the logical choice because then the am/pm status simply becomes another column in the time construct that obeys the usual rollover rules (okay, it mentions the rollover bit, but in a different way). And it should say that it is necessary to know and use this convention with many electronic devices, including computers. (In fact, it is for that very purpose that people look up am and pm in the first place!!!) And ultimately, there is nothing wrong about 12pm being noon and 12am being midnight. That's just the way it is. You need to learn how to spell, even though spelling is confusing. Similarly, you need to learn that 12pm is noon and 12am is midnight at the beginning of the day.
If you differ with me on this, can you PLEASE answer the questions I have posed? thanks. --Alan E. Feldman 2005-12-24 06:06 UTC.
When most people hear PM they think day light becuase the PM (12:00h or 12:00PM) starts in the daylight. When most people hear AM they think dark becuase the AM (00:00h or 12:00AM) starts at night.Perhaps I am oversimplifying this old and dead issue -greataff
- Not so they haer the numbers like they hear the numbers in the 24-hour clock.
The new write-up for "Amguity at noon and midnight" is much better than the previous versions I remarked on above. I'd like to add that I have been seeing increasing use of 12 PM for noon (and also one occurrence of 12 AM for midnight) over the last year or so. And I haven't seen any mistakes! It looks like we are finally beginning to break away from the original archaic defintions of am and pm -- as we should be. Alan E. Feldman 16:27, 2 July 2006 (UTC)
I am flabbergasted at this discussion in which the consensus seems to be that 12:00 a.m. is midnight and 12:00 p.m. is noon. This is exactly backwards from, for instance, the U.S. GPO Style Manual, which states:
9.54. References to meridian in statements of time are abbreviated as follows:
10 a.m. (not 10:00 a.m.) 2:30 p.m. 12 a.m. (formerly 12 m.) (noon) 12 p.m. (midnight)
Fitzaubrey 18:47, 15 September 2006 (UTC)
Your link gives a blank page. I'll check it again on Monday (or the next time I remember, if later). Anyway, what you quote makes no sense. There's a problem with writing "10:00 a.m."?
And what sense does it make to have
11:58 am 11:59 am 12:00 am 12:01 pm
be the standard? A digital clock shows 12:00 for 60 seconds. For all but the first instant of that period it is clear that its am/pm is the opposite of the minute before it. So why should the first instant of that period be different? The sequence
11:58 am 11:59 am 12:00 pm 12:01 pm
makes far more sense. This way, the am/pm field is simply just another column (though out of place) that follows the usual rollover rules. Why would anything else be any better? Every digital clock that uses am/pm assumes that 12:00 am is midnight and 12:00 pm is noon. It is the de facto convention, and rightly so. I have seen increasing use of 12:00 pm in signs and notices and such to mean noon and never the other way around. The American Heritage dictionary says 12:00 am is midnight and 12:00 pm is noon. Alan E. Feldman 2006-Nov-24 6:30 UTC.
Somebody changed the opening sentence for the "Confusion at noon and midnight" section to "The abbreviations for the terms ante meridiem (before noon) and post meridiem (after noon) should not be applied to noon and midnight." Why? This is obviously controversial. The previous statement (last seen on Aug 1) was much better, and certainly far more neutral. Why not say that use of am and pm at noon and midnight is highly controversial or that some claim that am and pm shouldn't be used for noon and midnight because their literal translations and so on. Then the "However, ..." part would follow nicely. In fact, the way it reads now is self-contradictory. It says that am and pm should not be used for noon and midnight, and then immediately gives very good reason why they should be used for noon and midnight. Why do some people find it so important to apply a literal translation of Latin terms to time when said terms originated hundreds of years ago when people used Local Solar Time and analog clocks as opposed to the elaborate system of Standard Time with time zones, daylight saving time, digital clocks and the like that we use today? Where are these people when it comes to the terms A.D. and B.C.? Using the same logic with these terms would cause the current Gregorian calendar to completely fall apart since no one knows for certain when Christ was born. Can someone please explain why the literal translations should be used for ante meridiem and post meridiem but not for Anno Domini and Before Christ? And what horrors would ensue if we would simply all accept the de facto, and quite sensible, new definitions of am and pm? It's not like we're redefining 2 plus 3 to be minus 97! Alan E. Feldman 2006-12-15 16:55 UTC.
I fixed the noon and midnight section. There is no reason that am and pm shouldn't be used for 12:00 noon and midnight. In fact at midnight it is actually an advantage in that it obviates the ambiguity of which midnight is being referred to: at the beginning of the day or at the end. Alan E. Feldman 2006-12-22.
(I'm sorry this entry is so long, but I'm trying very hard to be clear.)
Marcus Kuhn removed my addition "(Note that, according to the de facto convention, 12:00 a.m. does unambiguously refer to the beginning of the day.)" because he says that it is ambiguous. He missed the part that said "according to the de facto convention". The de facto convention is what the article refers to as "common practice". But the article is slightly incomplete because ***according to the de facto convention***, 12:00 am is the midnight at the beginning of the day. It is equivalent to, in 24-hour format, 00:00, not 24:00. In fact, if you create a file on your computer at midnight, you will see that I am right. So the article should really say instead:
"However, it has become common practice in countries that use the system (such as the United States) to define 12:00 am as the midnight at the beginning of the day (equivalent to 00:00 in the 24-hour notation) and 12:00 pm as noon (equivalent to 12:00 in the 24-hour notation)."
So, 12:00 am is ambiguous _only_ without the de facto convention. With the de facto convention, it is 100 percent unambiguous, which is what I was saying.
OK, so because the article incorrectly omitted the fact that 12:00 am is the midnight at the beginning of the day, I understand why Marcus deleted my statement. So I think the article should be fixed so that somehow it clearly explains that 12:00 am is at the beginning of the day. (Why is it at the beginning of the day? Because then the am/pm "column" follows the normal rollover rules of ordinary numbers. Explicitly, when the minutes column goes from 59 to 00, the hour is incremented by one. When the hours column goes from 11 to 12, the am/pm column is "incremented". When the am/pm column goes from pm to am, the day is incremented by one. It is 100% mathematically logical if you simply think of 12 as 0, AM as 0, and PM as 1. That is why 12:00 am is at the beginning of the day. It is also the easiest way to implement time in a digital or computer clock and is consistent with the "applies immediately after" part of the article..)
Despite the continuing efforts of the "literalists" (those who decree that you can never under any circumstances use am or pm at 12:00), despite the fact that they insist on engraving the original archaic, obsolete definitions of ante meridiem and post meridiem in stone for all eterninty, despite the fact that said terms originated in an era when Local Solar Time was in use which is completely different from the Standard Time system we use today, despite the fact that they have no problem with Anno Domini being applied to our current calendar system even though it suffers from ambiguity for ALL years; a new definition is taking hold, whether they like it or not. First digital clocks, and then computers, combined with logic, common sense, mathematical sense, etc., have practically forced this de facto convention upon us. Not only that, I see it being used more and more in train schedules and the posting of business hours. And I've never seen 12:00 am or 12:00 pm used incorrectly in such things in recent years (I think I saw it used wrong once many years ago, but I've also seen a huge number of words spelled wrong and an even larger number of apostrophe errors). Since this de facto convention is literally taking over, I think it should be clearly and correctly explained in this article. That is what would help people most when they encounter a situation in which they need to know what 12:00 am or pm means, not how obselete archaic terms don't apply.
If sources like Wikipedia, NIST, etc., would simply state correctly what the de facto convention is, THAT would be the most helpful. The literalists are doing us no favors by brining up the problem of noon not being before or after itself without acknowledging and explaining the de facto convention. The terms ante meridiem and post meridiem originated some 400 years ago and applied to a *different* timekeeping system. It's time to move on. The second has been redefined at least once. The meter has undergone at least four redefinitions. Would the world end if we acknowledge and carefully document the de facto convention for am/pm?
Don't get me wrong. If someone wants to point out that am and pm don't literally tell us how to assign themselves to 12:00 noon and midnight, fine. If someone wants to explain tricks like 11:59pm, 12:01 am, and such (and use such tricks), fine. But don't do it instead of clearly and correctly explaining the de facto convetion for am and pm. I'm sorry to have written at such length, but I find that's what it takes for me to be clear on this point. Alan E. Feldman 2007/01/02 UTC.
Oops! I got carried away with my "despite..."'s and screwed up. I meant that the literalists "insist on engraving the original archaic, obsolete definitions of ante meridiem and post meridiem in stone for all eterninty despite the fact that said terms originated in an era when Local Solar Time was in use which is completely different from the Standard Time system we use today" and "despite the fact that they have no problem with Anno Domini being applied to our current calendar system even though it suffers from ambiguity for ALL years"; not that the de facto convention is taking over because of these "despite..."'s. Now, to clarify the de facto convention: 12:00 am is 00:00 (the beginning of the day) in the 24-hour format and 12:00 pm is 12:00 in the 24-hour format (noon). There is no ambiguity in the definition; there is only ambiguity because some people are unaware of this convention. The sooner we all acknowledge it, the sooner the confusion will end. Alan E. Feldman 2007/01/14
It is unfortunate the the Chicago Manual of Style and the govt. publication cited in the article don't go with the de facto convention. They need to get with the times. Every computer using the 12-hour am/pm format uses the de facto convention as far as I know. And since computers are so dominant today, why do anything differently? If you see a file on your computer dated January 14, 2007 12:00 am, that means it was the beginning of January 14. If you see a file on your computer dated at 12:00 pm, you know that means noon. Since it would be highly impractical to reprogram all 12-hour computers and rewrite the time stamps of all 12:00 files, why on earth would it not be best to always use the de facto convention (given that one is already using the 12-hour am/pm clock, of course)?
BTW, the link to the gov't site (ref. 3) goes to a blank page and the link to the Chicago Manual of Style goes to a page that says nothing about 12:00. It does say not to use a.m. or p.m. with "o'clock" but to use morning, afternoon, evening, or night instead (8:00 a.m., but eight o'clock in the morning). Well, that won't work in the land of the midnight sun! (OK, the midnight-sun remark is a nitpick.) Alan E. Feldman 2007/01/14
Phrase needs verification
In chapter "Confusion at noon and midnight" it says
[begin quote] Noon and midnight are only infinitesimal points in time, and therefore it is not practical to use any other convention than that which also applies immediately afterwards, when the clock still displays 12:00. This convention is standardized for computer usage in American National Standard ANSI INCITS 310 (which extends the international standard ISO 8601 time notation with a 12-hour a.m./p.m. variant for the U.S.-market). [end quote]
The version of ANSI INCITS 310 which is currently available at [ansi.org] (go to the shop, search for INCITS 310) does not deal with the 12 hour format at all. It gives some explanation on how to use the 24 hour format in data exchange in the U.S., but no clarification, description or explanation on the 12 hour format. Where does the information given above come from? Was an explanation of the 12 hour format contained in a different version? Is the reference wrong? Or should the last sentence of this phrase rather be deleted from the article? Daisy G 12:37, 21 December 2006 (UTC)
- I recall having found sometimes in 1997 in the standards room of the Purdue University Engineering Library an ANSI standard that looked very similar to a national adoption of ISO 8601, but had also a 12-h notation option as an extention. I do not recall the exact document reference, whether it was "ANSI INCITS 310" or some predecesor of it, or whether what I found then is still a currently active ANSI standard as of 2006. Someone with easy access to a US library with a good ANSI collection might be able to answer this one. (ANSI standards are not easily available here in Britain.) It would be nice to have the correct reference and a description of what that specification did with midnight and noon. Sadly, the web sites of most standards bodies are very bad at providing access to information about historic documents. Markus Kuhn 15:46, 1 January 2007 (UTC)
- The standard I meant was probably ANSI X3.43-1986 "Representations of local time of day for information interchange" (also FIPS PUB 58-1) or ANSI X3.51-1975 "Representations of Universal Time, local time differentials, and United States time zone references for information interchange" (also FIPS PUB 59), but it seems that these FIPS documents were withdrawn in 1997 [1]. So the only US standard now left for representing time in information interchange is essentially identical to ISO 8601. (Given the various ambiguities inherent to the am/pm notation, that's certainly a wise choice, IMHO.) Markus Kuhn 08:22, 23 January 2007 (UTC)
Begin and end of day (24:00 issue)
The article contains this line:
- Some people dislike the idea that midnight has two different notations in the 24-hour clock, depending on whether it is the beginning (00:00) or end (24:00) of the day.
Under which user 155.208.231.234 added:
- This seems an odd argument to someone growing up with the 24 hour system, as we know that even though it is a TWENTYFOUR hour system, the time will never be displayed as 24. From 23:59:59, the time shifts to 00:00:00. Midnight will never be referred to as "at 24 o'clock" in writing nor in speech. In speech it is always "midnight", in wirting it can be referred to as "midnight" or in the format hh:MM (00:02 for two minutes past midnight).
This comment ignores the fact that written notices often contain 24:00 to explicitly indicate the end of the day. For example in ranges used for opening hours as from 07:00 to 24:00. See also the example of a time table using the 24:00 as well as the 00:00 notation in 24 hour clock. −Woodstone 15:16, 22 December 2006 (UTC)
Fix Citation needed
I regularly look at articles that are in need of citation and find links were I can give it the appropriate citation , thereby making wikipedia more encyclopedic , this article has proved problematic it only has one {{fact}} tag and when trying to check it out I can get to ISO 8601 and look at it, however ANSI standards seem to be for purchase and I cannot access the relevant info to allow me to remove the citation needed tag, if anyone out there can help out or maybe even look at rewording the article it seems like a simple job to remove this tag and yet without relevant links info etc I cannot do it. So for all those sharp minds out there I hope one or more of you can get on the case thanks --Matt 08:08, 17 January 2007 (UTC)
12:01
Is there any information on what the various sources saying that noon should be something other than 12:00 pm, have to say about 12:01, 12:30, etc? --Random832(tc) 13:27, 31 January 2007 (UTC)
Table of Time Values
Is there a need for the P.M. numbers to be complete, when the A.M. section is abbreviated with ellipses? I would like to have a uniform and concise table, and one that would be uniform (if possible) with the chart that would replace the one found at 24-hour clock...--Vox Rationis 00:30, 2 February 2007 (UTC)
Digital decoders' time notation
Are there any providers of cable or satellite television that still use the 12-hour notation in their set-top boxes? I ust want to find out which pay television companies have 12-hour time and which ones have 24-hour time. Scott Gall 04:40, 8 February 2007 (UTC) PS: My one uses 24-hour.