Purposes
Clocks are in homes, offices and many other places; smaller ones (watches) are carried on the wrist; larger ones are in public places, e.g. a train station or church. A small clock is often shown in a corner of computer displays, mobile phones and many MP3 players.
The 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 (see: counter). However, in this context, it is APPOINTMENT REMINDER SOFTWARE more appropriate to refer to it as a timer or trigger mechanism rather than strictly as a clock.
Computers depend on an accurate internal clock signal to allow synchronized processing. (A few research projects are developing CPUs based on asynchronous circuits.) Some computers also maintain time and date for all manner of operations whether these be for alarms, event initiation, or just to display the time of day. The internal computer clock is generally kept running by a small battery. Many computers will still function even if the APPOINTMENT REMINDER SOFTWARE internal clock battery is dead, but the computer clock will need to be reset each time the computer is restarted, since once power is lost, time is also lost.
[edit] Ideal clocks
An ideal clock is a scientific principle that measures the ratio of the duration of natural processes, and thus will give the time measure for use in physical theories.[citation needed] Therefore, to define an ideal clock in terms of any physical theory would be circular. An ideal clock is more appropriately defined in relationship to the set APPOINTMENT REMINDER SOFTWARE of all physical processes. An ideal clock should too measure time in consistent, for example decimalized time units.
This leads to the following definitions:
* A clock is a recurrent process and a counter.
* A good clock is one which, when used to measure other recurrent processes, finds many of them to be periodic.
* An ideal clock is a clock (i.e., recurrent process) that makes the most other recurrent processes periodic.
The recurrent, periodic process (e.g. a metronome) APPOINTMENT REMINDER SOFTWARE is an oscillator and typically generates a clock signal. Sometimes that signal alone is (confusingly) 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 successive levels of smaller and smaller error tolerances. While not all physical processes can be surveyed, the definition should be based on the set of physical processes which includes all individual physical processes which are proposed for consideration. Since atoms are so numerous and since, within APPOINTMENT REMINDER SOFTWARE current measurement tolerances they all beat in a manner such that if one is chosen as periodic then the others are all deemed to be periodic also, it follows that atomic clocks represent ideal clocks to within present measurement tolerances and in relation to all presently known physical processes. However, they are not so designated by fiat. Rather, they are designated as the current ideal clock because they are currently the best instantiation of the definition. APPOINTMENT REMINDER SOFTWARE
