BREIL 3S10 Mode D'emploi page 12

I TACHYMETER*
J TELEMETER
0
* Not available on all models
8
The tachymeter is used to measure the speed of an automobile.
By knowing how many seconds it takes for the vehicle to travel
one kilometre, the tachymeter can measure the approximate
average speed in km/h during a journey (over a maximum
measurable time of 60 seconds).
If the chronograph is started at the same time as the start of the
distance measurement and stopped after one kilometre, the
average speed can be calculated from the position of the
second hand. If the vehicle covers a distance of one kilometre in
45 seconds, then the average approximate speed is 80 km/h.
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.