Speedometer watch: what it is, how it works, and how to use it

A guide to the watch tachymeter, focusing on its operation, use, reading the tachymeter scale, and the most famous models that integrate this complication.

Among the most iconic graduated scales in watchmaking, the tachymeter holds a prominent place. Found mainly on chronograph watches, this particular scale allows for quick calculations of average speed over a known distance. Although today it is often associated with the aesthetics of sports and automotive watches, the tachymeter was born as a functional tool, designed to offer immediate measurement without recourse to complex calculations.

Understanding what a tachymeter is in a watch, how it works, and how to use it allows one to appreciate one of the most representative complications in technical watchmaking, still present today in numerous high-end models.

What is a tachymeter and what is it used for?

A watch tachymeter is a graduated scale, generally engraved on the bezel or the outer edge of the dial, that allows for the calculation of the average speed traveled over a predetermined distance, usually one kilometer or one mile.

The watch tachymeter always works in conjunction with the chronograph function: it measures the time taken to cover a certain distance and automatically converts that value into an average speed expressed in kilometers or miles per hour.

When asking what a tachymeter is for in watches, the answer is mainly related to speed measurement. However, thanks to the mathematical principle on which it is based, the tachymeter scale can also be used to calculate production frequencies or other repetitive activities distributed over an hour.

For this reason, the tachymeter has become one of the most appreciated complications in watches dedicated to motorsport, aviation, and, more generally, in fields where speed and precision of measurements play a fundamental role.

How does a watch tachymeter work?

To understand how watch tachymeters work, it is necessary to start from the principle that governs the tachymeter scale. This is based on a mathematical formula that relates the time taken to cover a unit of distance to the average hourly speed. The scale is already calibrated to perform this conversion automatically.

The operation of the watch tachymeter therefore involves the use of the chronograph. It is important to remember that the tachymeter only works correctly for times under 60 seconds, as the scale is designed for measurements within one hour.

How is the tachymeter used in watches?

Knowing how to use the tachymeter in watches means correctly using the chronograph together with the tachymeter scale. The procedure is quite simple:

• Start the chronograph when you begin to cover a known distance (for example, one kilometer);

• Stop the chronograph at the end of the distance;

• Observe where the chronograph seconds hand stops on the tachymeter scale.

The indicated value represents the average speed maintained during the journey. The same principle can also be applied to calculate other repetitive quantities. This versatility explains why the wrist watch tachymeter has historically been used not only in the automotive sector but also in industrial and professional fields.

How do you read the tachymeter?

Reading the tachymeter means correctly interpreting the values reported on the graduated scale. The numbers on the bezel do not represent the elapsed time, but rather the average speed automatically calculated based on the time measured by the chronograph. For example:

• 60 seconds correspond to 60 km/h;

• 45 seconds indicate approximately 80 km/h;

• 30 seconds correspond to 120 km/h;

• 20 seconds equate to 180 km/h.

The scale is generally decreasing: as the time taken increases, the average speed decreases. A correct reading always requires that the distance covered is known beforehand. Otherwise, the value returned by the scale would lose its meaning.

Tachymeter and chronograph: what are the differences?

Very often, the tachymeter and chronograph are confused, but they are two distinct elements. The chronograph is the mechanism that allows measuring time intervals using dedicated pushers and additional hands. The tachymeter, on the other hand, is the graduated scale that uses the time detected by the chronograph to automatically calculate an average speed.

In other words, the chronograph is the time-measuring function, while the tachymeter is a conversion tool. It is this close relationship that explains why the tachymeter is found almost exclusively on chronograph watches. Without the chronograph function, the tachymeter scale could not be used.

Watch with tachymeter: the most famous models

Throughout history, numerous Maisons have created iconic watches with tachymeters, which have become true benchmarks in sports watchmaking.

Among the most famous models is the Omega Speedmaster Moonwatch Professional, probably the most famous chronograph with a tachymeter in the world, also chosen during NASA's Apollo missions.

Another absolute reference is the TAG Heuer Carrera Chronograph, born in the 1960s for the world of automobile racing and still today a symbol of the link between chronography and motorsport.

The Rolex Cosmograph Daytona also represents one of the most iconic examples of a watch with a tachymeter, thanks to its characteristic graduated bezel which has become a distinctive element of the model.

Among the high-end watchmaking proposals, the Breitling Navitimer B01 Chronograph, which combines the tachymeter scale with other functions dedicated to aviation, and the Zenith Chronomaster Sport, appreciated for the high precision of its high-frequency chronograph movement, also deserve a mention.

Tachymeter and chronographs: the tradition of high watchmaking

The watch tachymeter represents one of the most emblematic complications of the chronograph tradition. Born to meet practical needs for speed measurement, today it continues to distinguish some of the most iconic timepieces in high watchmaking, combining functionality, precision, and design.

To discover a selection of luxury watches from the most prestigious Maisons, including chronograph models equipped with a tachymeter scale, you can consult the extensive offering of Pisa 1940.