A.M., P.M. and 24 Hour Clock - Explained Simply

A.M. or P.M. is the abbreviation that tells us whether the time occurs in the morning, or the afternoon or the evening. A. M occurs in the morning and stands for ante meridian which means "before midday" / "before noon". While P.M. occurs in the evening and stands for post meridian which means "after midday" / "afternoon".

In the A.M. / P.M. system of time which is what you used or used to seeing is a 12-hour clock is being used that means that morning goes till 12 hour noon. It starts over again at one o'clock and goes through 12 o'clock at midnight.

In contrast to it, a 24-hour clock does not start over the afternoon. The next which we normally think of at 1 o'clock is 1300 then 1400 and so on. Time goes all the way up until 2400 midnight which is also be called zero hundred because it is the start of the next day.

So what is 8 p.m. on a 24-hour clock? Eight p.m. is after noon so this is seven hours past twelve o'clock. We can simply say 12+8=20. So, the answer is 2000. It should be noted that a.m. and p.m.
are not used in the 24-hour clock.

Why A.M. and P.M.?

During ancient time, the people were used to measure the time by using a sundial clock, but it was quite difficult as people were able to identify time only during a particular period of the day. The decision to
divide a day into two cycles which is 12 hours was influenced by the fact that the moon also had 12 cycles.

When Is A.M. and When Is P.M.?

One of the most common problems of A.M. and P.M. was the confusion regarding the start of a day. To avoid the confusion regarding the denomination of noon and midnight, the convention refers to 12 A.M. as midnight and 12 P.M. as noon.
The most common reason in favor of 12-hour convention is easy pronunciation. It is easier to pronounce 6 P.M. rather than 18 hours. Hence, the use of A.M. and P.M. is more of an effective decision.

12 vs 24 Hours

It is being decided that 12 hour clock system can be used informally, in the conversation but in legal documents, schedules, and other interactions that require high precision time identification should follow the 24-hour format to avoid confusion with noon and midnight. 

Considering the 24-hour clock as the most effective system of timekeeping and used for high precision coordination, the international organizations managed to provide the most effective solution. The International Organization for Standardization (ISO) proposed to implement one format for the information exchange. 

Therefore, the standard ISO signify that all countries should use the specific format to indicate date and time (24-hour clock) and it should be used for documentation and formal communication.

Written by - Parul Verma 

Edited by - Anusha Vajha

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