History
The ancient Egyptians divided the day into 24 hours. There are diagrams of circles divided into 24 sections in the astronomical ceiling in the tomb of Senemut.
Sundials use some or all of the 24 hour dial, because they show the position of the sun in the sky. Sometimes, for aesthetic rather than practical reasons, all the 24 hour marks are shown.
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 In northern Europe, the Double XII system was gradually superseded during the 14th and 15th centuries by the single XII (12-hour system), leading to the widespread adoption of the 12-hour dial for popular use.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. 24 hour dials were also used on sidereal clocks, such as on this example by Charles Frodsham:
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.
In the 20th century, the 24 hour analog dial was adopted by radio amateurs, pilots, submariners, and for military use.
Read more about this topic: 24-hour Analog Dial
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