BREIL OS20 Mode D'emploi page 13

F TACHYMETER
The tachymeter is the device which measures the speed of an automobile. Knowing in
how many seconds the car covers a distance of 1 km, the meter can measure the
approximate average speed per hours during a journey (up to the maximum measurable
range of tachymeter which is 60 seconds).
If the chronograph is started at the same time as measurement, and stopped after 1 km,
the average speed per hour can be determined according to the position of the second
hand. If the car covers the distance of 1 km in the 45 seconds, the average hourly
speed during the journey will be about 80 Km.
TELEMETER
The telemeter is a distance indicator which allows distance to be calculated on the basis
of the speed of sound. It is useful, therefore, for aviation, navy, army and artillery
purposes. It can also measure how far away a thunderstorm is.
The hand is started the second a flash, smoke or lightning is seen and stopped when
the actual sound is heard. The distance, from 1 to 20 kilometres, between the observer
and the explosion or storm is read from the telemetry scale.
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