Tachymeter , tachymeter scale (also: tachometer, tachometer scale)
Clock function / scale for measuring speeds.
The tachymeter uses the reciprocal proportional relationship between time and speed to measure the (average) speed if the distance (= reference / base) is known .
The ring scale shows speeds for different time periods.
If, for example, the second hand of a chronograph is started when a milestone is passed by car , the speed can be read on the tachymeter scale when the next milestone is reached, if the milestones are set at a distance of the reference value (here 1 km). If the distance of exactly 1000 meters was covered in 40 seconds, for example, the average speed is 90 km / h, because v = s / t, i.e. v = 1000 m / 40 seconds = 25 m / s, that makes 25 · 3 , 6 km / h = 90 km / h. The tachymeter scale with the reference value of 1000 meters therefore indicates the number 90 at 40 seconds.
|km / h||∞||1000||700||500||400||350||300||270||240|
|km / h||220||200||180||160||150||140||130||120||110|
|km / h||100||95||90||85||80||75||70||65||
Witch this information you can easily calculate your average speed with just a watch on the wrist.