BSL Physics Glossary - timer - definition
A timer is a device for measuring lengths of time. For example to work out the speed of a moving object we need to know the start and finish time. Nowadays most timers have electronic digital displays. But in the past the timer was like a second hand on a watch, with a start / stop button at the top. We still use that sign. You may actually use an electronic display or a button on your watch that you press. The sign for all these devices is like the old-fashioned push button timer.