[. . . ] TACHYMETER INSTRUCTIONS The tachymeter scale enables the speed of a moving body to be read off in km/h (or in some other unit of measurement). [. . . ] Although it is marked "kmh" for kilometers per hour your tachymeter can also be used to measure "mph" or other units per hour. It can calculate how many cars per hour pass a given point on the highway, or how many units roll off a production line per hour. Assume you wish to measure a car's average speed over a one mile course. Let's say the car covered one mile or one kilometer in 45 seconds. The tachymeter number next to the 45 second mark is 80 ­ so the car averaged 80 miles per hour, or 80 kilometer per hour, over that measured course. To Determine Units per Hour: Start the stopwatch, count a convenient number of units and then stop the watch. [. . . ] Multiply 10 times 80 to get the number of units produced per hours: 800 1. [. . . ]