Re: 24-hour vs. 12-hour time, ambiguity, and abbreviations (was Re: Default date output format changed after an upgrade to buster)
On Thu 12 Sep 2019 at 09:42:03 (-0400), The Wanderer wrote:
> On 2019-09-12 at 06:30, Dan Ritter wrote:
> > David Wright wrote:
> >>
> >> What surprised me is the use of 12am and 12pm in the States. When I
> >> was at grammar school (in the days of 12hour times), you lost marks
> >> for writing either of these contradictions. It was either 12 noon,
> >> 12 midnight, or 12 o'clock (where there's no ambiguity).
> >
> > 12 o'clock is the only one of those which is ambiguous.
> >
> >> Even more astonishing is the fact that the US Government switched
> >> their am/pm meanings sometime between 2000 and 2008, which shows
> >> just how ambiguous they are.
> >
> > There is only one sensible interpretation:
> >
> > If 11:59 AM is two minutes before 12:01 PM, then 12:00 is PM.
> >
> > If 11:59 PM is two minutes before 12:01 AM, then 12:00 is AM.
>
> I take a slightly different approach, based on the apparent actual
> meanings of the words for which "AM" and "PM are abbreviations.
>
> It seems intuitively obvious to me that between 11:59 Ante-Meridiem and
> 12:01 Post-Meridiem must lie 12:00 Meridiem. (Though 12:00:01 - one
> second later - would be Post-Meridiem again.)
>
> Similarly, though less an "obvious necessity" consequence, between 11:59
> Post-Meridiem and 12:01 Ante-Meridiem lies 12:00 Midnight. (I understand
> "meridiem" to be derived from a word which would have literally meant
> "mid-day".)
Meridies (nominative case in Latin).
> Both are intuitively represented as "12:00 M" - with no "A" or "P" - and
> that, in its turn, is ambiguous.
It might be ambiguous if m were also an abbreviation for midnight,
which I've never come across. One can understand why, in the days of
12-hour clocks, midday was something distinctive, whereas the
precise time of midnight (as contrasted with "the middle of the night")
was largely irrelevant.
Many of the times we use were originally derived from counting the
hours after dawn: logical to the way people lived their lives.
So people took their siesta at the sixth hour and monks prayed in
nones at the ninth, mid-afternoon (ironically: noon, like the
start of the new year, has since drifted).
> That being part of why I stick with 24-hour time whenever possible.
When I read emails, I only see the Date: line from the header, and
the timedates used in the quotation lines. One thing I find odd is
mixing AM/PM with hours containing a leading zero. I was always
taught that 7 p.m. or 7pm was not written as 07, but I see that a
lot here. Contrast
$ TZ=Europe/Paris date +'%I.%M %p'
06.01 PM
$ TZ=Europe/Paris date +'%l.%M %p'
6.01 PM
$
> > The problem stems from 12 actually indicating what anybody sensible
> > would consider 0.
>
> As is likely part of the reason why the usual 24-hour clock goes from
> 23:59 to 00:00, yes.
Not forgetting 23:59:60 on occasions.
Cheers,
David.
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