Fourth dimension - AM/PM vs 24 Hour Clock

Usually fourth dimension is shown as Hours:Minutes

In that location are 24 Hours in a Solar day and lx Minutes in each 60 minutes.

Example: 10:25 means 10 Hours and 25 Minutes

Showing the Fourth dimension

There are ii main ways to testify the time: "24 Hr Clock" or "AM/PM":

24 Hour Clock: the time is shown as how many hours and minutes since midnight.

AM/PM (or "12 Hour Clock"): the mean solar day is split into:

  • the 12 Hours running from Midnight to Noon (the AM hours), and
  • the other 12 Hours running from Apex to Midnight (the PM hours).

Like this (endeavour the slider):

measure/images/time-am-pm.js

day am pm

AM

PM

Ante Meridiem*
Latin for "before midday"

Post Keridiem*
Latin for "after midday"

Midnight to Noon

Apex to Midnight

24 Hour:
00:00 to xi:59

24 Hour:
12:00 to 23:59

*Is that spelled "Meridiem" or "Acme"? See here.

Converting AM/PM to 24 Hr Clock

Add together 12 to any 60 minutes later on Noon (and subtract 12 for the start hour of the day):

For the offset hour of the 24-hour interval (12 Midnight to 12:59 AM), subtract 12 Hours

Examples: 12 Midnight = 00:00, 12:35 AM = 00:35

From ane:00 AM to 12:59 PM, no alter

Examples: 11:20 AM = 11:20, 12:30 PM = 12:xxx

From 1:00 PM to 11:59 PM, add 12 Hours

Examples: 4:45 PM = xvi:45, 11:50 PM = 23:50


Converting 24 Hour Clock to AM/PM

For the first 60 minutes of the day (00:00 to 00:59), add together 12 Hours, make it "AM"

Examples: 00:10 = 12:10 AM, 00:xl = 12:40 AM

From 01:00 to 11:59, only make information technology "AM"

Examples: 01:15 = one:fifteen AM, 11:25 = xi:25 AM

From 12:00 to 12:59, just make information technology "PM"

Examples: 12:ten = 12:10 PM, 12:55 = 12:55 PM

From 13:00 to 23:59, decrease 12 Hours, get in "PM"

Examples: fourteen:55 = 2:55 PM, 23:30 = 11:30 PM

Comparison Nautical chart

Here is a side-by-side comparison of the 24 Hour Clock and AM/PM:

Example: on the 60 minutes


Example: 10 minutes past

24 Hour Clock

AM / PM

24 Hour Clock

AM / PM
00:00 12 Midnight
00:10 12:ten AM
01:00 one:00 AM 01:10 i:x AM
02:00 2:00 AM 02:10 2:ten AM
03:00 3:00 AM 03:10 3:10 AM
04:00 4:00 AM 04:x 4:ten AM
05:00 5:00 AM 05:10 5:10 AM
06:00 6:00 AM 06:10 6:x AM
07:00 7:00 AM 07:x vii:10 AM
08:00 8:00 AM 08:ten 8:x AM
09:00 9:00 AM 09:10 9:x AM
10:00 10:00 AM ten:10 10:x AM
eleven:00 11:00 AM 11:ten 11:10 AM
12:00 12 Noon 12:10 12:10 PM
13:00 1:00 PM xiii:10 i:ten PM
14:00 2:00 PM 14:10 2:10 PM
fifteen:00 3:00 PM fifteen:10 3:10 PM
16:00 four:00 PM xvi:10 4:10 PM
17:00 5:00 PM 17:10 5:10 PM
xviii:00 vi:00 PM xviii:10 six:10 PM
19:00 7:00 PM 19:x 7:10 PM
20:00 8:00 PM 20:ten 8:10 PM
21:00 9:00 PM 21:x 9:10 PM
22:00 x:00 PM 22:ten ten:10 PM
23:00 11:00 PM 23:ten 11:10 PM

Midnight and Noon

"12 AM" and "12 PM" can cause confusion, and so we prefer "12 Midnight" and "12 Noon".

What Twenty-four hours is Midnight?

Midnight has another trouble: there is nix to tell us "is this the beginning or ending of the day".

holiday

Imagine your friends say they are leaving for holiday at "midnight" on 12th March, what twenty-four hours should you lot arrive to say adieu?

Do you get there on the 11th (assuming they leave at the very commencement of the twelfth), or the twelfth (bold they go out at the end of the 12th)?

Information technology is better to utilise:

  • xi:59 PM or 12:01 AM, or
  • 23:59 or 00:01 (24-Hour Clock)

which the railroads, airlines and military really do.

So, when you come across something like "offering ends midnight October 15th" tell them to use 1 infinitesimal earlier or after so there is no confusion!

Footnote on "Meridiem" vs "Elevation"

Should "AM" be "ante meridiem" or "ante meridian" (likewise for PM)?

The official (according to an American, Australian and British dictionary), and most mutual, spelling for AM is "ante meridiem" which is a Latin phrase. I recommend that spelling!

Just people sometimes use the phrase "ante meridian" (a "elevation" in this example refers to an imaginary line in the sky when the sunday is at its highest point).

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