| For example, the moment of midnight occurs precisely 12 hours after noon on the previous day and 12 hours before noon on the following day | Your friend could ask you to be at the airport at 12:01 am on April 13 or, if the following midnight is meant, at 11:59 pm on April 13 |
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| One account suggests that this custom evolved because the Egyptians commonly used the base 12, counting the 3 joints in their fingers, not including the thumb | The abbreviations am and pm derive from Latin:• To avoid any confusion when referring to the precise moment of noon or midnight, we recommend using the designations 12 noon and 12 midnight instead |
Starting at midnight, hours are numbered from 0 to 24, removing the need for designations like am and pm.
9| The main weakness of the 12-hour system is a widespread confusion about which abbreviation should be used for noon and midnight: neither moment can logically be identified as before noon am or after noon pm | From 12:01 pm to 12:59 pm, do nothing |
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| ; post meridiem is usually abbreviated PM, pm, p | To convert am or pm time to the 24-hour format, use these rules:• Although the precise moment of noon falls in neither category, the hour succeeding it, from 12:00:01 to 12:59:59, is clearly after noon |
Would you go there at midnight between April 12 and April 13? Most countries around the world today use the 24-hour system.
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