24 hour analog dial
Encyclopedia
Clocks and watches with a 24-hour analog dial have an hour
Hour
The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...

 hand that makes one complete revolution, 360°, in a day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...

 (24 hours per revolution). The more familiar 12-hour analog dial
12-hour clock
The 12-hour clock is a time conversion convention in which the 24 hours of the day are divided into two periods called ante meridiem and post meridiem...

 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 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
24-hour clock
The 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today...

.

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. http://commons.wikimedia.org/wiki/File:Pocket-sundial.JPG

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.

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
Senemut
Senenmut was an 18th dynasty ancient Egyptian architect and government official. His name translates literally as "mother's brother."- Family :...

.

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
Astrolabe
An astrolabe is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and longitude, surveying, triangulation, and to...

. In Northern Europe, the Double-XII system was preferred: two sets of the Roman numerals
Roman numerals
The numeral system of ancient Rome, or Roman numerals, uses combinations of letters from the Latin alphabet to signify values. The numbers 1 to 10 can be expressed in Roman numerals as:...

 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
John Harrison
John Harrison was a self-educated English clockmaker. He invented the marine chronometer, a long-sought device in solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long distance sea travel in the Age...

, Thomas Tompion
Thomas Tompion
Thomas Tompion was an English clock maker, watchmaker and mechanician who is still regarded to this day as the Father of English Clockmaking. Tompion's work includes some of the most historic and important clocks and watches in the world and can command very high prices whenever outstanding...

, and Mudge
Thomas Mudge (horologist)
Thomas Mudge was an English horologist who invented the lever escapement, the greatest single improvement ever applied to pocket watches.-Early life:...

 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
Sidereal time
Sidereal time is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky...

 clocks, such as on this example by Charles Frodsham
Charles Frodsham
Charles Frodsham was a renowned English watch and clockmaker. He took over Arnold & Co in 1843 at 84 Strand, London...

:
The famous Big Ben
Clock Tower, Palace of Westminster
Big Ben is the nickname for the great bell of the clock at the north end of the Palace of Westminster in London, and is generally extended to refer to the clock or the clock tower as well. It is the largest four-faced chiming clock and the third-tallest free-standing clock tower in the world...

 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.

Today

24-hour analog watches and clocks are still being manufactured today, and are sought after by collectors and enthusiasts. A famous brand is the Glycine
Glycine Watch
Glycine is a Swiss wristwatch manufacturer. Glycine became a noteworthy watch maker in the early 1950s for the introduction of their Airman model, a 24 hour watch favored by both military and commercial pilots. The Airman was worn by many U.S. Air Force pilots during the Vietnam War. Glycine still...

 Airman watch. Other manufacturers who make 24-hour analog watches include Breitling
Breitling
Breitling is a luxury brand of Swiss watches produced by Breitling SA, a private company headquartered in Grenchen, Canton of Solothurn . The company exclusively offered Certified Chronometers in all models since 2000...

, Raketa
Raketa
Raketa watches have been manufactured since 1962 by the Petrodvorets Watch Factory in Saint Petersburg. The Petrodvorets Watch Factory is Russia's oldest factory, it was founded by Peter the Great in 1721 as the Peterhof Lapidary Works to make hardstone carvings...

, Vostok
Vostok watches
Vostok Watch Makers, Inc. produces mainly rugged military and diver mechanical watches at its factory in Chistopol, Tatarstan, Russia...

, Fortis
Fortis Uhren AG
Fortis is a watchmaker founded and based in Grenchen Switzerland that was established by Walter Vogt in 1912.- History :12 years after its establishment, Walter Vogt set up production with John Harwood, the inventor of the automatic wristwatch. In 1926, Fortis released the first self-winding...

, Poljot
Poljot
Poljot , is a brand of Soviet/Russian wristwatches, produced since 1964 by the First Moscow Watch Factory . The flagship brand of the USSR's watch industry, Poljot produced numerous historical watches used in many important space missions, including the world's first space watch worn by Yuri Gagarin...

, Swatch
Swatch
Swatch is a brand name for a line of wrist watches from the Swatch Group, a Swiss conglomerate with vertical control of the production of Swiss watches and related products...

, and many others.

Design

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.

In the United States, the government and military commonly use 24-hour clocks having noon at the bottom; the variant with noon at the top is far less common.

World time

A common use for the 24-hour analog method of representing time is for showing the way the time of day depends on one's location. A globe, map, or disk can be used.

In fiction

George Orwell
George Orwell
Eric Arthur Blair , better known by his pen name George Orwell, was an English author and journalist...

 uses the 12-hour and 24-hour dials to symbolize the old and new worlds in his novel Nineteen Eighty-Four
Nineteen Eighty-Four
Nineteen Eighty-Four by George Orwell is a dystopian novel about Oceania, a society ruled by the oligarchical dictatorship of the Party...

. The 12-hour dial is a relic of pre-revolutionary society, used to represent the desirable past; the 24-hour dial and time system is the compulsory standard imposed by the Party, and represents both conformity and the undesirable nature of the new world. This theme is famously set in the opening line:
It was a bright cold day in April, and the clocks were striking thirteen.


In the 1927 film Metropolis
Metropolis (film)
Metropolis is a 1927 German expressionist film in the science-fiction genre directed by Fritz Lang. Produced in Germany during a stable period of the Weimar Republic, Metropolis is set in a futuristic urban dystopia and makes use of this context to explore the social crisis between workers and...

, the opening scene shows both a 24-hour analog clock and a 10-hour (metric) analog clock, one above the other. Both are used to convey the impression of an alien and highly efficient society.

External links

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