What is the name of the scale on some chronograph dials that measures distance?

The scale that is specifically designed to measure distance on some chronograph dials is known as the telemetric scale. This scale is particularly useful for calculating how far away a sound event occurs, such as a thunderclap, by using the difference in time between seeing the flash of lightning and hearing the thunder.

When using a chronograph with a telemetric scale, the user starts the chronograph timer as soon as they see the event (like the lightning), and once they hear the sound, they stop the timer. The distance can then be read directly from the telemetric scale based on the elapsed time—typically, every second corresponds to a certain number of kilometers or miles.

Understanding the telemetric scale's function helps watch enthusiasts appreciate the dual purpose of chronographs: timing and measuring specific events, enriching the overall experience of using these timepieces.