It’s probably the obsessive-compulsive nerd in me, but I’ve always hated the 12-hour clock system. It’s so illogical, with two of each hour number during each day. I admit I’ll say “six o’clock” rather than “eighteen hundred hours” in general conversation, but for appointments, schedules or anything that refers to an accurate time, I use 24-hour notation.
The 12-hour clock probably originated with the Babylonians, since they were keen on the numbers 12 and 60. It’s known that the ancient Egyptians used it, and then, much later, the Romans used a system of dividing the night and day each into 12 equal hours. That meant that daytime hours were longer in Summer and shorter in Winter, with nighttime hours doing the reverse.
That irregular system would have been difficult to replicate mechanically, so the first clockwork devices abandoned the idea and split the day into 24 constant, equal hours. The earliest clocks had dials with 24 divisions, although some numbered them in two twelves. Others, for example the clock face on the ancient church of San Giacomo in Venice, used numbers 1 to 24. (Though on San Giacomo, the digit 1 is approximately where we would put 4. Oh, I get it: 12 and 24 are on the horizontal axis, and 6 and 18 are on the vertical. Neat.)
Later in the Middle Ages, the 12-hour display began to oust the 24-hour one on public clocks, and the end result is that the 12-hour dial is now standard, even in countries where 24-hour usage is more common. (According to Wikipedia, only 17 countries in the world prefer 12-hour time notation, including, of course, the United States.)
One thing that bugs me in particular about 12-hour time is the notation for midday and midnight. Actually, I literally don’t know if 12:00 a.m. is midday or midnight. Since “a.m.” is from “ante meridiem”, or “before noon”, you’d assume that it couldn’t be noon, and would therefore be midnight. But that would leave the other one with “p.m.” or “post meridiem”, meaning that noon is “after noon” — obvious nonsense. Reverse the argument though, and it’s exactly equal nonsense.
In fact, I’ve just looked it up and 12:00 a.m. is generally taken to mean midnight. Therefore, you have the absurdity of each half of the day being numbered 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11.
24-hour time cuts through all of that ambiguity and lack of logic, which is why it’s loved by nerds. The first standards for e-mail, all the way back to the 1970s, specified 24-hour notation for times even though they were invented in America; and on the Internet today, everything works that way. (I’m told that if you have a Microsoft Windows computer and set the language to “Swahili”, the clock converts to 12-hour.)
Famously, the other thing that Americans do wrong is to write dates as month/day/year, when from the nerd point of view, it should be in sequence from smaller division to larger, or indeed from larger to smaller. In fact, of those two options about two-thirds of the world’s population uses day/month/year and one third (China and Japan, for example) uses year/month/day. Nerds actually prefer the latter, because a sequence of dates in that form will sort into sequence with a simple textual sort. (For example, all my photographs are in folders named like 2011-03-27-something).
Converting the USA to 24-hour times and sortable dates is but a futile dream, but already some of Europe has gone the whole hog, at least officially, by adopting ISO 8601. That’s the international standard for specifying dates and times, and it was written by nerds. I like it.