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.
| at sec | zero | 3.60 | 5.14 | 7.20 | 9.00 | 10.29 | 12.00 | 13.33 | 15.00 |
| km / h | ∞ | 1000 | 700 | 500 | 400 | 350 | 300 | 270 | 240 |
| at sec | 16.36 | 18.00 | 20.00 | 22.50 | 24.00 | 25.71 | 27.69 | 30.00 | 32.73 |
| km / h | 220 | 200 | 180 | 160 | 150 | 140 | 130 | 120 | 110 |
| at sec | 36.00 | 37.89 | 40.00 | 42.35 | 45.00 | 48.00 | 51.43 | 55.38 | 60.00 |
| km / h | 100 | 95 | 90 | 85 | 80 | 75 | 70 | 65 |
60 |
Witch this information you can easily calculate your average speed with just a watch on the wrist.