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). Measure the time taken to travel one kilometer (or a different unit) and read the
result on the tachymeter scale. For example, the time taken is 40 seconds, equivalent to a speed of 90
km/h. You use your tachymeter to measure rates of speed. 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. Here’s how it works:
To Measure Speed of Travel:
1. Assume you wish to measure a car’s average speed over a one mile course. Start the stopwatch
when the car passes the starting point. Stop it when the car passes the one-mile or one-
kilometer mark.
2. Read the corresponding number on the outer tachymeter ring. 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:
1. Start the stopwatch, count a convenient number of units and then stop the watch. Say, for
example, that you are counting units of production and you stop the count at 10 units, and the
sweep seconds hand reads 45 seconds.
2. The tachymeter number next to the 45 second mark is 80. Multiply 10 times 80 to get the
number of units produced per hours: 800
