How does the tachymeter scale work?
A tachymeter is used for measuring speed and was applied when cars did not have a tachometer yet. For measuring speed a measured section of one mile is required. The chronograph is started at a mile marker. At the next mile marker, the point on the scale adjacent to the second hand indicates the speed (in miles per hour) of travel between the two mile markers. So the tachymeter scale is a scale, which measures the speed=path/time(v=s/t); the speed is indicated in miles per hour.
