Timing complication
What is a telemeter?
A chronograph scale that turns the delay between seeing an event and hearing it into a distance, using the speed of sound.
How it works
Start the chronograph when you see lightning or a flash and stop it when you hear the sound. The telemeter scale converts the time into distance, because sound travels about 343 metres a second at 20°C. Three seconds means about a kilometre.
Scales are usually in kilometres, sometimes miles. The speed of sound changes with temperature, so the reading is approximate.
History
Telemeter scales were designed for artillery in the First World War, to estimate the distance of enemy guns, and later used to judge how far away a thunderstorm is.
Before you buy
Like the pulsometer, the telemeter is now mainly a vintage style detail, often printed as a spiral or outer ring on the dial.
Questions
- How does a telemeter work?
- It measures the time between seeing something and hearing it, then multiplies by the speed of sound, about 343 metres per second, to give a distance.