Me again replied: "I shamelessy copied and pasted this from the web. How To Use A Tachymeter Learning By Example - Here Is A Common Example Using A Tachymeter Measure the average speed a racecar is traveling. Start the chronograph function when the car passes the starting line, and stop the function after the car travels exactly one mile; noting esitionof the chronograph hand.In this example, the hand points to the 4 hour position (20 seconds elapsed). Now, looking beyond the 4 hour position to the Tachymeter dial face, reveals the number 180. The tachymeter indicates a computed speed of 180 MPH. Example 2) Observing a slow moving object. Since recorded time lapse must be between 7.2 and 60 seconds, the distance to travel for the recorded time must be short.. Example: It took 36 seconds for a sailboat to travel 1/10 a nautical mile. Reading the tachymeter dial, 100 knots is indicated. However, since 1/10 of a nautical mile was traveled, the actual answer is 1/10 of 100, equals 10 knots. Example 3) Observing a very fast moving object Example: A plane travels 10 kilometers, in 10 seconds. The tachymeter dial points to 360. Therefore, the answer is computed to 10 X 360; equals 3600 km/hour. Other Uses For A Tachymeter Dial A tachymeter can be used to measure gas consumption. Example: It took 50 seconds to burn up 1 gallon of gasoline. Reading the tachymeter scale at the moment 1 gallon was consumed, reveals the number 72. This computes to 72 gallons of fuel per hour is being consumed. With more experience using this easy tool, a user will quickly realize the usefulness of a tachymeter."