Tachymeter watch

Tachymeter

— a device for measuring the speed of movement (and some other speeds), used in watches with arrows on the dial. Usually it has the form of a special scale printed on the bezel; and the speed is determined by the time of passage of the measured section or the execution of 1 standard process / cycle. Most often, modern tachymeters are marked based on a measured section one standard unit long and speed in such units per hour — for example, using this function on a section 1 km long, you can determine the speed in km/h.

The presence of a tachymeter, by definition, means that the watch is equipped with a chronograph or at least an arrow-type stopwatch (see the relevant paragraphs). And when determining the speed, the stopwatch hand counts the time of passage of the measured section from zero on the tachymeter; the division on this scale, which it will indicate after stopping the countdown, will correspond to the measured speed.

Note that this feature has its limitations. In particular, the measurement time should not exceed 1 minute — otherwise the second hand will go to the second circle, and the final readings will not correspond to reality; and the higher the measured speed, the lower the accuracy. In fact, this means that a tachometer can more or less reliably measure speeds not lower than 60 km (or other units) per hour and not higher than 400, or even 300 kilometers (units) per hour. Nevertheless, even such features are often very useful.