What is a Tachymeter?

Nowadays, tachymeters are a common feature on high-end watches, and even if most watch owners don’t know it is there, this feature is, in fact, a key component of many modern chronograph watches. What exactly is a tachymeter? What does it measure? How do you use it?

"Tachymeter", is a word originated from the Greek language, tachos (speed) and metron (measure). Basically, a tachymeter is a mechanism for measuring speed. It does this by using a scale that marks the time elapsed and converts it into the speed travelled. A tachymeter works in conjunction with a chronograph, or a stop watch. The tachymeter can be found around the watch’s rim or bezel where it’s calibrated to show the number of seconds in an hour – 3600.

Fixed Tachymeter

Quick Release Milanese Mesh Watch Band (View Detail) on the Vintage Omega Speedmaster Mark III

The chronograph button will be on the outer edge of the watch face. The very first chronograph was invented back in 1821 by a French watchmaker, Nicolas Mathieu Rieussec. However, the first chronograph wristwatch was not actually invented until 1913. Shortly after that, tachymeter was added.

Quick Release Revive Pilot Watch Band (View Watch Band)

This was a huge step forward and watches with this function became popular, particularly for those involved in aviation or automobile racing. The most common reason why one would use a tachymeter is to measure speed. In order to use it effectively, it is important to understand how tachymeter actually works.

Quick Release Tropic Rally Italian Leather Watch Band, the best match type of watch band for Tachymeter watch (view watch band)

To properly use a tachymeter on a fixed bezel watch, set the chronograph hand to zero and drive one kilometer before checking the read on the tachymeter. The reading from the results will be the average speed you have been moving in over that last kilometer. Tachymeter is calculated with a mathematical equation where you would divide 3600 (which is the number of seconds in an hour), by the number of seconds that it takes a vehicle to cover a measured mile or kilometer.

Tachymeter can also be found on Modern style Omega Speedmaster such as Dark Side of the Moon 311.92.44.51.01.003

For instance, lets say the tachymeter reads 90, this means you have taken forty seconds to travel that distance because: 3600/40=90. Now that we know the basics with how tachymeter works, lets talk about the different types of them and how they work.

Snail-Type Tachymeter

A legend class of Tachymeter watch - 1940s Philippe Watch Chronograph Ref. 2519 With Snail Dial (image credit)

Another type of tachymeter is the “Snail-type”. With the given name, snail-type tachymeters are best used to measure slower speeds (i.e. events that occur slower than 60 cycles per hour). What results instead is a tachymeter design that sort of spirals inward on the center of the dial allowing for a wider range of speeds since the scale it’s usable for multiple rotations of the second hand. Typically, this is present via three colored rings measuring times from 0 to 60, 61 to 120 and 121 to 180. On the other hand, if you’re looking to measure the speed of an airplane, or a race car, that will travel more than one mile in 60 seconds, you’ll need to use a tachymeter with a rotating bezel. First off, you’ll need to increase the fixed distance.(set from one mile to ten miles) .

Rotating Tachymeter Bezel

Breitling Navitimer 01 with Rotating Tachymeter Bezel (image credit)

Let's say an airplane takes 30 seconds to fly 10 miles. Your tachymeter will indicate a speed of 120 miles per hour. However, because the fixed distance is actually 10 miles and not 1 mile, you’ll multiple that tachymeter scale reading by 10 to calculate a speed of 1,200 miles per hour. As mentioned before, watches with tachymeter are often used by pilots and race car drivers. However, this particular feature has been made obsolete with the advancements of technology where a high tech stopwatch or some other similar electronic gadget. This feature is little more than a stylish addition used to offset other elements of a watch. Particularly common in chronograph watches, this feature is a classic element of this style. Many feel that a 'chrono' without a tachymeter is not a true chronograph at all. Guess it all comes down to your personal preference.

Written by Sam , images by Toni and others as noted