Timekeeping in d20

The d20 game has for a long time had a unique system of timekeeping, based on the need to count relatively short but human-scale units of time. This system meshes interestingly with the traditional Chinese system of twelve two-hour watches.

The smallest unit of time is a second. There are 6 seconds in a round, 10 rounds in a minute, 10 minutes in a turn, 12 turns in a watch, and 12 watches in a day. The terminology may vary according to the edition of the game.

In southern temperate latitudes (say, between Boston and Miami), sunrise and sunset varies over the course of the year, by about an hour and a half in the south and about three hours farther north. In Atlanta, Georgia, it's very close to two hours. For gameplay purposes, it'd be a simple abstraction to rule that the sun rises in the fourth watch and sets on the tenth watch. This would be very nearly true in Atlanta if the first watch started at 11:30pm rather than midnight. The timezones make some things simpler, but not necessarily the accurate assessment of true solar noon and solar midnight.

A pendulum with a period of two rounds (which would count one round per swing) would be about 36 meters long; a pendulum with a period of one round (which would count a half-round every swing) would be about 9 meters long.