The telemeter graduation on the case ring or on the dial of chronographs is used to measure the distance of an immediately visible and later audible event (e.g. lightning and thunder, waving and calling, fireworks and firecrackers, etc.). The classification on the telemeter scale is calculated on the basis of a speed of sound of 343 m/s in air at 20 °C.
- With rotating telemeter ring, set zero position to 12:00.
- Start the stop function with pusher 4 when the visible event occurs.
Press pusher 4 again when the sound becomes audible.
In the example below, the thunderstorm is still 3 km away.