A tachymeter is a scale inscribed on the bezel or the outer edge of a watch dial, used to measure speed based on time traveled over a fixed distance. It is a crucial feature in chronograph watches, allowing the wearer to calculate speed in units per hour, such as kilometers or miles, without the need for electronic devices. To use a tachymeter, the chronograph function is started at a known starting point, and once the wearer reaches the endpoint of a measured distance, the chronograph is stopped. The position of the second hand on the tachymeter scale will indicate the speed. For example, if it takes 30 seconds to travel one kilometer, the tachymeter scale will show a speed of 120 units per hour. This tool is particularly useful for pilots, race car drivers, and other professionals who require quick and accurate speed calculations. The tachymeter scale is typically calibrated to measure speeds ranging from 60 to 400 units per hour, making it versatile for various applications. Its presence on a watch not only adds functionality but also enhances the aesthetic appeal, often associated with precision and technical sophistication in horology.