PM Full Form

What is the full form of PM?

The full form of PM is Post Meridiem. It is a notation of time for the period after noon. The notation is of use only when dealing with the time stated on a 12-hour clock, since it repeats an hour twice a day. Therefore, in order to be able to distinguish between 3 at noon and at night, the terms 3 p.m. and 3 a.m. are put to use.

This Story also Contains

1. What is the full form of PM?
2. Origin of PM
3. Significance of PM (Post Meridiem)
4. Comparison between 12 and 24-hour clock
5. Country-wise Uses

The 12-hour clock was popularised by the Romans in which the 24 hours of the day were separated into two periods. The Romans separated the time into 12 same hours, repeated twice, and denoted either A.M. (Ante Meridiem) or P.M. (Post Meridiem). They also started the tradition used worldwide today, of the new day starting at midnight.

Origin of PM

The word “post meridiem” has been derived from the Latin language. Its literal translation corresponds to “after midday”. It is a term that finds its use in the 12-hour clock system. Although the term is Latin, the 12-hour system can be traced back to ancient Egypt. The tomb of Pharaoh Amenhotep I included both an Egyptian water clock for use at night and a sundial for use during the day. These clocks, which date to around 1500 BC, divided each of their different times of usage into 12 hours.

The 12-hour clock was also used by the Romans, who divided the day into 12 equal hours (resulting in hours that varied in length throughout the year) and divided the night into four watches.

Significance of PM (Post Meridiem)

PM, or post meridiem, is only useful while reading time from a 12-hour clock. In a 24-hour clock, each hour of the day has a different number assigned whereas, in a 12-hour clock, the numbers are repeated after midday. The time span from midday to just before midnight, i.e., from 12:00 pm until 11:59 pm is represented by PM on the 12-hour clock. Therefore, to understand whether the time being referred to is before midday or after midday, the terms AM (Ante Meridiem or before midday) and PM (Post Meridiem or after midday) are used. For example, if someone has to explain that an event occurred at 2 in the afternoon, one can either refer to it as the event occurred at 14 hours or at 2 pm.

The 12-hour dial, on which the shorter hour hand rotates twice per day and once every 12 hours, is used by the majority of analog clocks and watches today. However, computers typically display the time in 24-hour notation by default. For a select few language and region settings, the majority of operating systems, including Microsoft Windows and Unix-like systems like Linux and macOS, enable the 12-hour notation by default.

Comparison between 12 and 24-hour clock

The main difference between a 12-hour and a 24-hour clock is that the former has only 12 numbers to represent 24 hours. Therefore the hour hand makes two rounds of the clock per day and the same time is repeated twice. However, in a 24-hour clock, each hour of the day has a unique number assigned to it, and the digits after 12 refer to the time past midday, represented as PM in the 12-hour clock. The comparison between the time as shown in the 12-hour and 24-hour clock is as shown below-

Country-wise Uses

The majority of nations that were a part of the former British Empire, such as the United Kingdom, Republic of Ireland, United States, Canada (excluding Quebec), Australia, New Zealand, South Africa, India, Pakistan, and Bangladesh, as well as other countries such as Mexico and the former American colony of the Philippines, use the 12-hour clock as the primary written and spoken system of the time. However, the 24-hour clock remains the prevalent timekeeping method worldwide, particularly for written communication. Some countries in Europe and Latin America combine the two, favoring the 12-hour system for informal communication while utilising the 24-hour system in writing and professional settings.