Tuesday, October 25, 2011

Comparison Chart of Times

http://www.mathsisfun.com/time.html

Comparison Chart

Here is a side-by-side comparison of the 24-hour system and 12-hour system (AM/PM):
         
Example: on the hour
Example: 10 minutes past
24-hour system
AM / PM
24-hour system
AM / PM
         
0:00 12 Midnight
0:10 12:10 AM
1:00 1:00 AM   1:10 1:10 AM
2:00 2:00 AM   2:10 2:10 AM
3:00 3:00 AM   3:10 3:10 AM
4:00 4:00 AM   4:10 4:10 AM
5:00 5:00 AM   5:10 5:10 AM
6:00 6:00 AM   6:10 6:10 AM
7:00 7:00 AM   7:10 7:10 AM
8:00 8:00 AM   8:10 8:10 AM
9:00 9:00 AM   9:10 9:10 AM
10:00 10:00 AM   10:10 10:10 AM
11:00 11:00 AM   11:10 11:10 AM
12:00 12 Noon   12:10 12:10 PM
13:00 1:00 PM   13:10 1:10 PM
14:00 2:00 PM   14:10 2:10 PM
15:00 3:00 PM   15:10 3:10 PM
16:00 4:00 PM   16:10 4:10 PM
17:00 5:00 PM   17:10 5:10 PM
18:00 6:00 PM   18:10 6:10 PM
19:00 7:00 PM   19:10 7:10 PM
20:00 8:00 PM   20:10 8:10 PM
21:00 9:00 PM   21:10 9:10 PM
22:00 10:00 PM   22:10 10:10 PM
23:00 11:00 PM   23:10 11:10 PM

Midnight and Noon

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

What Day is Midnight?

Midnight has another problem - there is nothing to tell you "is this the beginning or ending of the day".
Imagine you are told your friends are leaving for holiday at "midnight" on 12th March, what day should you arrive to say goodbye? Do you get there on the 11th (assuming they leave at the very start of the 12th), or the 12th (assuming they leave at the end of the 12th)?
It is better to use:
  • 11:59 PM or 12:01 AM, or
  • 23:59 or 0:01 (24-Hour Clock)
which the railroads, airlines and military actually do.
So, if you see something like "offer ends midnight October 15th" tell them to use one minute before or after so there is no confusion!


Example:

Converting AM/PM to 24-hour system

   
  For the first hour of the day (12 Midnight to 12:59 AM), subtract 12 Hours
    Examples: 12 Midnight = 0:00, 12:35 AM = 0:35
     
  From 1:00 AM to 12:59 PM, no change
    Examples: 11:20 AM = 11:20, 12:30 PM = 12:30
     
  From 1:00 PM to 11:59 PM, add 12 Hours
    Examples: 4:45 PM = 16:45, 11:50 PM = 23:50

Converting 24-hour system to AM/PM

     
  For the first hour of the day (0:00 to 0:59), add 12 Hours, make it "AM"
    Examples: 0:10 = 12:10 AM, 0:40 = 12:40 AM
     
  From 1:00 to 11:59, just make it "AM"
    Examples: 1:15 = 1:15 AM, 11:25 = 11:25 AM
     
  From 12:00 to 12:59, just make it "PM"
    Examples: 12:10 = 12:10 PM, 12:55 = 12:55 PM
     
  From 13:00 to 23:59, subtract 12 Hours, make it "PM"
    Examples: 14:55 = 2:55 PM, 23:30 = 11:30 PM


1 comment:

  1. I always confuse the 12am and 12pm in 24-hour system.
    After read this post, i can understand easily!

    ReplyDelete