A clock mechanism may be used to control a device according to time, e.g. a central heating system, a VCR, or a time bomb (see: digital counter). Such mechanisms are usually called timers. Clock mechanisms are also used to drive devices such as solar trackers and astronomical telescopes, which have to turn at accurately controlled speeds to counteract the rotation of the Earth.

Some clocks, usually digital ones, include an optical projector that shines a magnified image of the time display onto a screen or onto a surface such as an indoor ceiling or wall. The digits are large enough to be easily read, without using glasses, by persons with moderately imperfect vision, so the clocks are convenient for use in their bedrooms. Usually, the timekeeping circuitry has a battery as a backup source for an uninterrupted power supply to keep the clock on time, while the projection light only works when the unit is connected to an A.C. supply. Completely battery-powered portable versions resembling flashlights are also available.
In 1283, a large clock was installed at Dunstable Priory; its location above the rood screen suggests that it was not a water clock.[citation needed] In 1292, Canterbury Cathedral installed a 'great horloge'. Over the next 30 years there are mentions of clocks at a number of ecclesiastical institutions in England, Italy, and France. In 1322, a new clock was installed in Norwich, an expensive replacement for an earlier clock installed in 1273. This had a large (2 metre) astronomical dial with automata and bells. The costs of the installation included the full-time employment of two clockkeepers for two years.[citation needed]
This item is a new-Never removed from box-SEIKO brand musical and movement wall clock. Clock and packaging in mint condition. Plays 24 different melodies and the 6-piece dial opens and turns during hourly melodies. Rotating pendulum and dial has Swarovski crystal components. This is the now retired “Special Collector’s Edition” considered one of the finer of the melodies clocks! Batteries are included. Comes from pet and smoke free home. As always Thank you for your interest!
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“Great alarm clock for the price. Gigantic numbers for my old eyes. Very basic, easy to set, just what I wanted. Alarm is loud even on low [with] an awful sound that would wake the dead. But that sound makes me get right up, so it does exactly what it’s supposed to do. If you want a soft gentle caress to wake you, get something else, but this is a good alarm and easy to use.”