Wristwatches with a stopwatch function often feature a tachymeter. This is why sporty chronographs are usually equipped with it, but this function can also be found on normal watches. Many watches have the tachymeter on the bezel, but it can also be found directly on the dial. In this case, numbers from 500 to 60 can be found. The word is derived from the ancient Greek terms tachýs and métron and means scale or measure. The tachymeter is used to determine speeds. To do this, a previously defined distance must be determined over which the speed is to be measured. Usually 1 km is marked out. The average speed is then displayed on the scale by the stopped second hand. If the scale is designed to display kilometres per hour, it can be used to read how fast a car is driving, for example. The function displays the reciprocal of the hour that has passed since the measurement began. After 30 seconds, for example, 1/120th of an hour has passed and the value 120 is then displayed on the scale. The car is therefore travelling at 120 km/h. To determine the correct speed, the second hand must be stopped at exactly the right moment. To do this, it is first activated at the 12 o'clock position and then stopped again after one kilometre. Since this cannot be determined quite accurately by humans, the display of the tachymeter is more of a guide value.
