24-hour analog dial

Tower clock in Martinengo, province of Bergamo, Lombardy. The 24th hour on the right side of the dial is typical for the old Italian time system of 24 hours counted from dusk.
A sundial showing all 24 hours; impractical but symmetrical
Shepherd Gate clock outside the Royal Observatory, Greenwich
The clock at Ottery St Mary, England, showing nearly noon, using the 12-hour time system on a 24-hour analog dial
The 24-hour tower clock in Venice that uses double-XII system

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). The more familiar 12-hour analog dial has an hour hand that makes two complete revolutions in a day (12 hours per revolution).

Twenty-four-hour analog clocks and watches are used today by logistics workers, fire fighters, police officers, paramedics, nurses, pilots,[1] scientists,[2] and the military,[3] 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.

Sundials use 24-hour analog dials—the shadow traces a path that repeats approximately once per day. Many sundials are marked with the double-XII or double-12 system, in which the numbers I to XII (or 1 to 12) are used twice, once for the morning hours, and once for the afternoon and evening hours. So VI (or 6) appears twice on many dials, once near sunrise and once near sunset.

Modern 24-hour analog dials—other than sundials—are almost always marked with 24 numbers or hour marks around the edge, using the 24-hour clock system. These dials do not need to indicate AM or PM.

  1. ^ ""Glycine Watch"". Archived from the original on 2011-07-11. Retrieved 20 February 2018.
  2. ^ "Sidereal Clock". bmumford.com. Retrieved 13 May 2024.
  3. ^ ""Marathon Marine clock designed for military use"". Archived from the original on 2012-03-10. Retrieved 20 February 2018.