A timer is a specialized type of clock that is used to measure specific time intervals. Timers can be classified into two main types. A timer that counts up from zero to measure elapsed time is often called a stopwatch, while a device that counts down from a specified time interval is usually called a timer. A simple example of this type is an hourglass. Operating method timers have two main groups: hardware and software timers. Most timers give an indication that the time interval that has been set has expired. Time switches, time mechanisms that activate a switch, are sometimes called "timers".
