We explain what the acronyms a mean. m. And p. m. and its equivalence with the 24-hour system. Also, how do you indicate 12 noon.
What do the acronyms stand for? m. And p. m.?
In the twelve-hour time system, the dominant system in the world, the day is divided into two equal segments of 12 hours each, called a.m (from the Latin "before noon"), abbreviated to. m.; Y post meridian (from the Latin "after noon"), abbreviated p. m.
In this way, the hours of each period are numbered from 0 to 12, and these two abbreviations are used to distinguish them from each other. Thus, 8 a.m. m. equals 8 in the morning, while 8 p.m. m. equal to eight o'clock in the evening. The only exception to the rule is midday, since at 12 o'clock the acronym always accompanies m. (from Latin meridians, that is, “noon”).
These acronym they are always written accompanied by a period and separated by a space, and are often marked on watches and automatic alarm clocks. On the other hand, they are not used in the 24-hour time system, also known as the military time system, since in it the hours are counted from 00:00 to 24:00, without any margin of ambiguity. In some countries one system or the other is preferred, although the use of the 12-hour system is much more common.
The following is a table of equivalences between both systems:
| 24 hour system | 12 hour system |
| 00:00 | 12:00 a.m. m. |
| 01:00 | 1:00 a.m. m. |
| 02:00 | 2:00 a.m. m. |
| 03:00 | 3:00 a.m. m. |
| 04:59 | 4:59 AM m. |
| 06:30 | 6:30 a.m. m. |
| 12:00 | 12:00 p.m. |
| 13:30 | 1:00 p.m. m. |
| 14:50 | 2:50 pm m. |
| 17:00 | 5:00 p.m. m. |
| 22:22 | 10:22 PM m. |
| 23:00 | 11:00 p.m. m. |
| 23:59 | 11:59 PM m. |
This 12-hour system was the traditional time system inherited from classical antiquity, and was the only one in existence until the 19th century, when the Scottish-born Canadian inventor and engineer Sandford Fleming (1827-1915) proposed the 24-hour time , as part of the creation of universal standard time, that is, of the system of time zones to determine the time anywhere in the world, using the Greenwich Meridian as a date change point.
Why is it used only m. to indicate 12 noon?
If the logic of the 12-hour time system is to divide the day into two equal blocks, one before noon (a.m.) and another after (p.m.), it is normal for doubts to arise as to which of the two blocks corresponds to noon, that is, 12 noon. And the answer is none, since the acronym is used for this case m. to indicate that it is precisely noon. On the other hand, for twelve at night, 12 a.m. is used. m., since this hour occurs at the beginning of the day, twelve hours before the day is halfway through.