Digital clocks display a numeric representation of time
Two numeric display formats are commonly used on digital clocks:
the 24-hour notation with hours ranging 00–23;
the 12-hour notation with AM/PM indicator, with hours indicated as 12AM, followed by 1AM–11AM, followed by 12PM, followed by 1PM–11PM (a notation mostly used in the United States).
Most digital clocks use an LCD, LED, or VFD display; many other display technologies are used as well (cathode ray tubes, nixie tubes, etc.)
After a reset, battery change or power failure, digital clocks without a backup battery or capacitor either start counting from 12:00, or stay at 12:00, often with blinking digits indicating that time needs to be set
Some newer clocks will actually reset themselves based on radio or Internet time servers that are tuned to national atomic clocks
Since the release of digital clocks in the mainstream, the use of analogue clocks has declined significantly.
Basic digital clock radio
For convenience, distance, telephony or blindness, auditory clocks present the time as sounds
The sound is either spoken natural language, (e.g
"The time is twelve thirty-five"), or as auditory codes (e.g
number of sequential bell rings on the hour represents the number of the hour like the bell Big Ben)
Most telecommunication companies also provide a Speaking clock service as well.
A rare Deutsche Bahn Train station clock
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