A tachymeter is a scale used on some watches, typically found on the bezel or dial. It allows the wearer to measure speed based on time traveled over a known distance. For example, if you know the distance is one kilometer, you can use the tachymeter to determine how fast you traveled that distance by reading the scale after timing yourself. This feature is especially popular in sports and racing contexts, where quick calculations are essential. Many luxury watch brands, like Rolex and Tag Heuer, incorporate tachymeters into their designs, making them not only functional but also stylish accessories for enthusiasts and professionals alike.