You can read the current speed on the tachymeter scale. For this, measure the time that you need for one kilometer. Then, the tachymeter scale indicates the speed. The minimum speed that can be measured by a tachymeter scale is 60 km/h. At this speed the second hand needs exactly one run over the face during the travelling time that is needed for one kilometer. Please check whether your watch is set on kilometers or miles per hour (km/h and mph).