David Wright wrote:
What surprised me is the use of 12am and 12pm in the States. When
I was at grammar school (in the days of 12hour times), you lost
marks for writing either of these contradictions. It was either
12 noon, 12 midnight, or 12 o'clock (where there's no ambiguity).
12 o'clock is the only one of those which is ambiguous.
Even more astonishing is the fact that the US Government switched
their am/pm meanings sometime between 2000 and 2008, which shows
just how ambiguous they are.
There is only one sensible interpretation:
If 11:59 AM is two minutes before 12:01 PM, then 12:00 is PM.
If 11:59 PM is two minutes before 12:01 AM, then 12:00 is AM.
The problem stems from 12 actually indicating what anybody
sensible would consider 0.