Clock

100 A clock is an instrument for measuring time. A clock is typically a physical instrument; an especially accurate one is called a chronometer. The clock in its current form has been in use since at least the 14th century. Clock can refer to a conceptual system of time measurement.

Purposes

A windup alarm clock Clocks are in homes and offices; smaller ones are carried; big ones are in civic places, e.g. a train station or church. A small clock is often shown in a corner of computer displays or mobile phones.

The major purpose of a clock is not always to display the time. It may also be used to control a device according to time, e.g. an alarm clock, a VCR, or a time bomb.

Practically all computers depend on an exact internal clock signal to allow synchronized processing. Some computers also maintain time and date for all manner of operations whether these are for alarms, event beginning or just to display the time of day.


Ideal uses
An ideal clock procedures the ratio of the duration of natural processes, and thus will give the time measure for use in physical theories. Therefore, to define an ideal clock in terms of any physical theory would be circular. An ideal clock is more suitably defined in relationship to the set of all physical processes.

A clock is a repeated, periodic process and a counter.
A good clock is one which, when used to measure other repeated processes, finds many of them to be periodic.
An ideal clock is a clock that makes the most other repeated processes periodic.
The recurrent, periodic process is an oscillator and typically generates a clock signal. Sometimes that signal alone is called "the clock", but sometimes "the clock" includes the counter, its indicator, and everything else supporting it.

This definition can be further improved by the consideration of succeeding levels of lesser and lesser error tolerances.