## Answer

###### Wiki User

###### 11/08/2008

**WHAT IT DOES** The tachymetre scale can be used to compute
many things, but it's primary purpose is to compute the speed after
noting how long it takes to travel a fixed distance (e.g. one mile
or kilometer). The dial is a scale which computes the function:
*Tachymetre Dial = 3600 / Elapsed Time in Seconds* The scale
is valid for all elapsed times from 7.2 seconds to 60 seconds. If
the duration of the event is outside this range, then the answer on
the dial is invalid. **HOW TO USE IT** For example, suppose you
wanted to measure the average speed a racecar was traveling. After
starting the chronograph function when the car passes the starting
line, and stopping it after the car travels exactly one mile, you
note that the chronograph hand is pointing at the 4 o'clock
position (i.e. 20 seconds have elapsed) Looking beyond the 4 to the
Tachymetre dial reveals the chronograph hand pointing at 180. This
means that the average speed of the car would be 180 MPH. Let's
say, instead of the race car speed, you are measuring something
much slower, like sailboat speed. In this case, you need to use a
shorter distance because the elapsed time must fall within the 7.2
- 60 seconds range. For this example, let's say it took 36 seconds
for your sailboat to travel 1/10 of a nautical mile. Reading the
tachymetre dial gives a speed of 100 knots. However, since we only
traveled 1/10 of a nautical mile, the actual answer is 1/10 of that
or 10 knots. Now let's say you wanted to measure the speed of a
VERY, VERY fast airplane: after traveling 10 kilometers, you noted
that 10 seconds have elapsed. The tachymetre dial gives an answer
of 360 but we traveled 10 Km. Therefore, the answer is 10X360, or
3600 km/hour. There is really nothing magic about using the
Tachymetre dial to measure speed. You can also use it to measure
other things, like gas consumption. Suppose it took 50 seconds to
burn up a gallon of gasoline. Reading the tachymetre scale shows
that you are burning 72 gallons of gasoline per hour