「午前 12時」が「12 P.M.」とか

12

まさか、 「11AM」 の一時間後が 「12PM」 だなんて...

よく見かけるので調べてみたら...


<?php
date_default_timezone_set('UTC');
//date_default_timezone_set('Asia/Tokyo');

for ($h = 0; $h < 24; $h++) {
  $time = $h * 60 * 60;
  printf('%s - %s - %s %s' . "\n",
         date('H:i',   $time),
         date('h:i a', $time),
         date('h:i A', $time),
         $h % 12 === 0 ? '*' : '');
}

PHP: date - Manual


00:00 - 12:00 am - 12:00 AM *
01:00 - 01:00 am - 01:00 AM 
02:00 - 02:00 am - 02:00 AM 
03:00 - 03:00 am - 03:00 AM 
04:00 - 04:00 am - 04:00 AM 
05:00 - 05:00 am - 05:00 AM 
06:00 - 06:00 am - 06:00 AM 
07:00 - 07:00 am - 07:00 AM 
08:00 - 08:00 am - 08:00 AM 
09:00 - 09:00 am - 09:00 AM 
10:00 - 10:00 am - 10:00 AM 
11:00 - 11:00 am - 11:00 AM 
12:00 - 12:00 pm - 12:00 PM *
13:00 - 01:00 pm - 01:00 PM 
14:00 - 02:00 pm - 02:00 PM 
15:00 - 03:00 pm - 03:00 PM 
16:00 - 04:00 pm - 04:00 PM 
17:00 - 05:00 pm - 05:00 PM 
18:00 - 06:00 pm - 06:00 PM
19:00 - 07:00 pm - 07:00 PM 
20:00 - 08:00 pm - 08:00 PM 
21:00 - 09:00 pm - 09:00 PM 
22:00 - 10:00 pm - 10:00 PM 
23:00 - 11:00 pm - 11:00 PM

まじか...

Usage Note: By convention, 12 AM denotes midnight and 12 PM denotes noon. Because of the potential for confusion, it is advisable to use 12 noon and 12 midnight.

American Heritage Dictionary Entry: PM

そうなのですか...

覚えておきます。