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12 P.M. - say what?

By Murray Bourne, 22 Dec 2005

I'm sure you have seen something like this:

The service will not be available from 8:00 A.M. to 12:00 P.M.

What does that end time mean? 12 noon? 12 midnight? It should mean "12 hours after the middle of the day" (P.M. stands for the Latin "post meridian"), so it must be midnight.


But what does 12 A.M. mean? (A.M. stands for "ante meridean", or "before the middle of the day".) Twelve hours before the middle of the day is also 12 midnight. So 12 A.M. = 12 P.M. = midnight. Not a good idea.

(True story) My mother was booked on a plane that was scheduled to leave at 12 P.M. on 5th January. What does that mean? It could be midnight as 5th January is starting, or midnight as 5th January is finishing, or many people take it to mean 12 noon on 5th January. My mother was there 12 hours too late and missed the plane.

Suggestion: Avoid arranging anything to start or end at noon or midnight (unless the context is very clear.) Use "noon" or "midnight" to reduce some of the confusion.

Footnote: In Singapore, they do a strange thing with TV schedules. They assume that the next day starts at 6:00 am. So the programs for today, 22nd Dec, go from 6:00 A.M. 22 Dec to 6:00 A.M. 23 Dec. It can be confusing when trying to set up DVD recordings for 2:00 A.M. The recorder date/time is correct, but the cable schedule is not.

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