Telemeter (clock)

A telemeter (from ancient Greek : τῆλε tēle "fern" and μέτρον métron "measure, measure") is the function of a chronograph to measure distances to events that emit both light and sound.

functionality

It is a scale on the dial or the bezel that uses the relationship between distance (s), time (t) and speed (v), more precisely the speed of light or the speed of sound :

${\displaystyle v={\tfrac {s}{t}}}$

converted to:

${\displaystyle s=vt}$

The speed of light and sound are almost constant within the earth's atmosphere, which means that the distance only depends on time. As soon as you see the event (e.g. a lightning bolt), the time measurement starts and when you hear (e.g. the thunder) the same event, the chronograph is stopped. Sound travels a kilometer in about three seconds in the air, while the flash of light takes a negligible three microseconds for the same distance. The distance in km can therefore be read off directly on the telemeter scale, i.e. the seconds displayed are divided by three.

history

The telemeter in chronographs was not primarily developed to estimate the distance to thunderstorms, but it was a military requirement to be able to determine the distance to the enemy relatively easily in times of war. Artillery muzzle flashes gave off an observable light effect and the time to the thunder of cannons was measured. Other applications were the distance measurement during bombing or torpedo hits. In naval clocks, the distance scale was in nautical miles.

Web links

• Telemeter Chronograph - How it Works , Video (2 min)

Individual evidence

1. ^ NN: Guns, lightning and thunder - they brought the telemeter scale. Uhrenkosmos GmbH, accessed on August 28, 2019 .