timer

A timer is a specialized type of clock used for measuring specific time intervals.
Timers can be categorized into two main types.
A timer which counts upwards from zero for measuring elapsed time is often called a stopwatch, while a device which counts down from a specified time interval is more usually called a timer. A simple example of this type is an hourglass.
Working method timers have two main groups: Hardware and Software timers.
Most timers give an indication that the time interval that had been set has expired.
Time switches, timing mechanisms which activate a switch, are sometimes also called "timers".

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