Q21. What is the tachymeter scale for?
A.To calculate average speed from the time it takes to travel 1km
The "tachymeter scale" (hereinafter tachymeter) is the scale on the bezel. It is one of the functions of the chronograph that can measure the time required to move 1km and calculate the average speed per hour for that section. By the way, the origin of the word is Tachy, which means fast, and Meter, which is a slide rule.
Daytona's tachymeter number was originally 200, but now it is a specification that can measure up to 400 (km).
The tachymeter number indicates the speed of 120 km/h at the 6 o'clock position, 60 km/h at the 60 second position (12 o'clock position), and so on. For conversion, it is the value obtained by dividing 3600 seconds, which is the number of seconds in one hour, by the number of seconds it took to move 1 km. Before the spread of airplanes, the tachymeter only had increments of about 100km at maximum, but since then the increments have become finer year by year. According to A. Lange & Söhne designer Reinhard Meiss, the maximum display was 500km until around 1940, 750km to 800km after the 1950s, and 1000km from the mid-1950s.
The way to use it is to start the chronograph at the same time as the measurement starts. Then stop at 1km point. At this time, the number on the tachymeter indicated by the chronograph second hand is the speed per hour.
Sentence ◎Yuki Matsumoto (editorial department)
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