A tachymeter is a scale that is sometimes inscribed around the rim of an analog watch with a chronograph). It can be used to measure the speed of a vehicle over a known distance. The tachymeter scale on a watch converts between the number of seconds it takes for an event to happen and the number of times that event will occur in one hour). To use a tachymeter-equipped watch for measuring speed, the chronograph is started at a starting marker of a known distance. At the next marker, the point on the scale adjacent to the second hand indicates the speed (in distance between markers per hour) of travel between the two). The tachymeter scale is rotated to align with the second hand at the start of the length to be measured. When the second hand reaches the point on the scale where the speed indicated equals the speed of the vehicle, one unit of distance (miles if speed is miles per hour, kilometers if speed is kilometers per hour) has been traveled). The tachymeter scale can measure times from approximately 7 seconds to 60 seconds. The scale on a watch is only valid for things that happen in 60 seconds or fewer, and the scale is also difficult to resolve for events that take fewer than 10 seconds or so to occur). A tachymeter-equipped watch can also be used to measure distance by timing the travel over the distance while the speed is held constant).