24 Hour Dial Views

• Watches

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. Note that this definition refers to the use of a complete circular dial to represent a 24-hour day. Using the numbers from 0 to 23 (or 1 to 24) to mark the day is the 24-hour clock system.

Medieval clocks often used the 24-hour analog dial, influenced by the widespread example of the astrolabe. In Northern Europe, the Double-XII system was preferred: two sets of the Roman numerals I to XII were used, one on the left side for the night and morning hours, and another set on the right side of the dial to represent the afternoon and evening hours. In Italy, the numbers from 1 to 24 (I to XXIV in Roman numerals) were used, leading to the widespread use of the 24 hour system in that country. On Italian clocks, though, the I was often shown at the right side of the dial, rather than the top. This probably reflects the influence of the Italian timekeeping system, which started counting the hours of the day at sunset or twilight.

In northern Europe, the Double XII system was gradually superseded during the 14th and 15th centuries by the single XII (12-hour system), leading to the widespread adoption of the 12-hour dial for popular use. The 24-hour analog dial continued to be used, but primarily by technicians, astronomers, scientists, and clockmakers. John Harrison, Thomas Tompion, and Mudge built a number of clocks with 24 hour analog dials, particularly when building astronomical and nautical instruments. The famous Big Ben clock in London has a 24 hour dial as part of the mechanism, although it is not visible from the outside.

The major variation in the design of 24-hour analog dials is the location of midnight and noon. Although always opposite each other, 180° apart, noon is sometimes at the top, sometimes at the bottom. A few rare variants place noon and midnight at the right and left sides. There is no ambiguity if the 24-hour numbering is used.