Nearly all sundials are inherently 24-hour analog dials - the "hour hand" shadow travels a path that approximately repeats once per day.However, most sundials are marked with the Double-XII system - in particular "XI" is marked near sunrise and repeated near sunset - using the 12-hour clock system. Many medieval clocks - and even a few modern ones - use 12-hour numbering rather than 24, even though the "hour" hand makes a single revolution in a day. Note that this definition refers to the use of a complete circular dial to represent a 24-hour day, not to the use of the numbers from 0 to 23 (or 1 to 24), the 24-hour clock system. ![]() Twenty-four-hour analog clocks and watches are used today by pilots, scientists, and the military, and are sometimes preferred because of the unambiguous representation of a whole day at a time. The more familiar 12-hour analog dial has an hour hand that makes two complete revolutions in a day (12 hours per revolution). Clocks and watches with a 24-hour analog dial have an hour hand that makes one complete revolution, 360°, in a day (24 hours per revolution).
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