12PM 是中午
记得我刚来美国的时候，有门课程12PM开始。当时我问教授怎么晚上那么晚了还上课。他笑着说12PM是中午。
其实，中国人中分不清楚12AM和12PM的大有人在。我相信很多人把12AM当成是中午，12PM当成晚上。就168肯定就有很多人分不清楚。
规则参看：钱多多选股大赛规则截止日期: 11/15/2009 12:00am EST.
报名截止。
所以我在规则里面，尽量不用12，都用11：59啥的。
Are noon and midnight 12 a.m. or 12 p.m.?
This is a tricky question. The answer is that the terms 12 a.m. and 12 p.m. are wrong and should not be used.
To illustrate this, consider that "a.m" and "p.m." are abbreviations for "ante meridiem" and "post meridiem." They mean "before noon" and "after noon," respectively. Noon is neither before or after noon; it is simply noon. Therefore, neither the "a.m." nor "p.m." designation is correct. On the other hand, midnight is both 12 hours before noon and 12 hours after noon. Therefore, either 12 a.m. or 12 p.m. could work as a designation for midnight, but both would be ambiguous as to the date intended.
When a specific date is important, and when we can use a 24-hour clock, we prefer to designate that moment not as 1200 midnight, but rather as 0000 if we are referring to the beginning of a given day (or date), or 2400 if we are designating the end of a given day (or date).
To be certain of avoiding ambiguity (while still using a 12-hour clock), specify an event as beginning at 1201 a.m. or ending at 1159 p.m., for example; this method is used by the railroads and airlines for schedules, and is often found on legal papers such as contracts and insurance policies.
If one is referring not to a specific date, but rather to several days, or days in general, use the terms noon and midnight instead of 12 a.m. and 12 p.m. For example, a bank might be open on Saturdays from 8 a.m. to noon. Or a grocery store might be open daily until midnight. The terms "12 noon" and "12 midnight" are also correct, though redundant.
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在中文，上午12点指的是中午12点。
不过在英文里，12AM是凌晨0点。
出国三年了，国外都是这样的。
我们不说多的。把自己的windows XP的右下角显示时间的东西调成12小时制前面加上AM PM(或上午，下午)显示。然后在等到中午12点，你就知道了。
