# How to use the tachymeter of your watch?

As you may have noticed, most chronograph watches have a curious scale around the dial or on their bezel.

But what exactly is the tachymeter scale used for and how does it work?

The tachymeter function is used to measure the average speed of an object or a person over a known distance. To use this function it is necessary to have a chronograph watch in order to be able to start and stop the time measuring.

## Small explanation...

First of all, it is up to you to choose the unit of reference for your tachymeter. Indeed, you can choose to measure in miles or kilometers, as long as the measurement is done over a distance of one mile or one kilometer. Indeed, on most chronographs, the unit of measurement is not indicated or it is simply engraved "UNITS PER HOUR".

We will therefore illustrate this with an example in which we will use the kilometer, this is also valid for the miles and you simply have to replace kilometers by miles in all our statements.

Let's say you're in a car and you drive past a mile marker. At that moment, you start the chronograph of your timepiece, the second hand starts its journey. Then, at the next milestone, you stop your chronograph and read the number on the tachymeter scale that the chronograph hand is pointing to. This number corresponds to your average speed between the two milestones (separated by one kilometer), this speed is given in kilometers per hour.

A very useful function to have fun measuring the average speed of your Aston Martin DB5. For now, you can wear it on your wrist thanks to the Atelier Jalaper watches. Watches inspired by the automobile not in their functions (well, not yet…) but in their composition and design. Each dial of Atelier Jalaper timepieces integrates a real piece of a legendary car.

But let's come back to our primary subject, the tachymeter. As we said, the measurement is done on a kilometer as previously mentioned and this is the case for most tachymetric scales. In fact, these scales indicate that the speed must be measured over a fixed distance of one kilometer. And when this distance is not explicitly indicated by the scale, it is often 1000m too.

Chronograph watches with tachymeter have different measuring scales:

- The first and most common is specified, specified because the required distance of measurement is indicated on the scale. As mentioned above, this distance is very often 1000m.

- The second is the unspecified scale, meaning that the scale is, as its name indicates, unspecified on the tachymeter, but that one must assume that a distance of 1000m will be used to make the measurement.

Finally there is the tachymeter with two scales indicating different graduations on the timepiece. We can find a first scale which has as a base a distance of 1000m and a second one which has as a base a distance of 100m.

At Atelier Jalaper we have a project to add a chronograph to our collection. Being the ultimate piece mixing automobile and watchmaking, we dreamed of being able to add the chronograph complication to our timepieces one day. We already have an idea of the legend we could use for this timepiece... By the way, what legend do you think could honor the chronograph function at AJ?