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This page is a stub. Eventually it will cover various types of clock.

Summary

Clocks have seen many changes with evolving technology.

Safety

You may miss your bus if your clock is wrong. This could really spoil your day.

Clockwork clocks

These are the oldest type of clock and are purely mechanical. After many years of service they often stop working because of wear in the bearings and gears. Repairing these is a highly skilled operation, if possible at all.

Electrically-assisted clocks

These have a pendulum or a balance wheel like a clockwork clock, but it's kept in motion electrically instead of by a spring.

Mains synchronous clocks

These run off the AC mains supply and rely for their accuracy on the fact that although the mains supply can vary slightly from its nominal 50Hz (or 60Hz in some regions), the total number of cycles in as day is very carefully controlled. (This is because if demand exceeds supply, all the generators tend to slow down under the load, or speed up in the case of over-supply. Hence the frequency is used as a vital tool in manageing the National Grid.)

Quartz clocks

These rely on the vibrations of a crystal of quartz for their time keeping, rather than a balance wheel or pendulum.

Radio-controlled clocks

These generally have a quartz clock mechanism for back-up timekeeping, but get an accurate time reference from a radio signal, such as MSF Rugby.

Flip-down clocks

These are the earliest widely available form of digital clock. The hours and minutes and possibly the day of the week and day of the month are displayed on flip-down cards.

7 segment display clocks

These may use a quartz crystal, radio signal or the 50Hz mains supply for the time standard.

Other types

All the commoner types of clock are listed above but there are others you might occasionally come across or may have heard about. These will either have a different time reference or a different type of display, or both.

GPS clocks

There are now several satellite based global positioning systems in addition to the original US GPS system, and they all rely on highly accurate clocks. A GPS receiver can hence provide an accurate time source just as eaily as a positional fix.

Internet clocks

Time sources are available on the Internet, and it is these that your computer or smartphone uses as the reference to periodically correct its internal quartz-based time source.

Atomic clocks

These are the most accurate time standards available but they are far too expensive for domestic use, and until recently, too bulky.

Nixie tube clocks

Nixie tubes were used as digital displays before LED-based 7-segment displays became widely available. A nixie tube consists of a glass envelope containing neon gas and 10 digits formed out of wire. Any one of these can be lit up by applying a voltage to it, causing it to glow with the characteristic orange neon glow. Nowadays these clocks are purely a novelty item, but popular amongst the maker community.

External links

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