A clock is simply a device for displaying time. Originally this included all methods of ascertaining time for example candle clocks, sundials, hour glasses, and water clocks known as clepsydra.
In modern parlance the term clock now generally refers to mechanical or electronic device which is not portable, thus excluding wristwatches and is designed to remain in a single established position. The earliest known truly mechanical clocks date from the 13th century although clocks with some form of mechanism were in existence from a much earlier period.
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