Telemeter scale on chronograph watch
Timing to 1/5 seconds.
Timing up to 30 minutes.
Timing telephone conversations.
Telemeter scale (R)
By means of the telemeter scale it is possible to measure the distance of a phenomenon which is both visible and audible. The chronograph hand is released at the instant the phenomenon is seen; it is stopped when the sound is heard, and its position on the scale shows at a glance the distance in kilometers or miles separating the phenomenon from observer. (Calibration is based on the speed at which sound travels through the air, viz, approximately 340 meters or 1,115 feet per second).
During a thunderstorm the time that has elapsed between the flash of lighting and the sound of the thunder is registered on the chronograph scale is illustrated on the opposite side. The distance between the observation point and the thunderstorm, in this case, is 1600 meters.
On this dial there is also a tachometer scale, which is shown by blue circles. This is used in the following way; if the minute-recording hand points to 0 the speed will be shown on the middle circle (speed between 60 and 30 kilometers); if the minute-recording hand points to 2 minutes the speed will be shown on the inside circle (speed between 30 and 20 kilometers).