Watch tachometer, how does it work ?

What is the purpose of a watch's tachymeter and how do you use it?

"What is the tachymeter used for on a watch? And above all, how does it work?" This is a question we often ask ourselves when faced with this graduated bezel so characteristic of... sports watches And chronographs.

Today, the Charlie Paris team sheds light on this watchmaking tool, which is as technical as it is intriguing.

What is a tachymeter in watchmaking? (Definition)

In the world of watchmaking, a tachymeter (or tachymetric scale) is a complication or graduation that allows the calculation of an average speed over a given distance.
Usually engraved on the outer bezel of the Case or present on the dial, it works in conjunction with the chronograph's seconds hand and generally expresses speed in kilometers per hour (km/h).

How does the tachymeter on a watch work?

The principle of using a tachometer is simple, but requires a minimum of timing. To measure speed (for example, in a car or on a bicycle between two kilometer markers):

• At the starting point (base 0): Activate the chronograph on your watch.
  
• At the finish line (1 kilometer further on): Stop the chronograph immediately.
  
• Read the result: Look at the position of the chronograph's seconds hand on the tachymeter scale. The number indicated corresponds directly to your average speed over that kilometer. Example: If the needle stops at the number 60, your average speed was 60 km/h.
  

The different types of tachometer scales

Not all tachymeter watches are created equal, and the scale can vary between models:

• The specified or unspecified scale (base 1,000 meters): This is the most common case. The scale is based on a fixed reference distance of one kilometer (1,000 meters).
  
• The two-level ladder: Some dials have several concentric graduations. The first is always based on 1,000 meters, while the second refers to a shorter distance of 100 meters, ideal for measuring speeds over short distances or very fast-moving objects.
  

Now you know everything about the tachymeter! Feel free to browse our Charlie Paris chronograph collections to sport this iconic horological complication on your wrist.