How do you use a tachymeter?

Start the chronograph as you pass the beginning of a known distance (one mile or one kilometer). Stop the chronograph at the end. Read the number on the tachymeter bezel where the chronograph second hand points — that number is your average speed in miles or kilometers per hour, depending on the distance unit you measured.

What is the formula for a tachymeter?

Speed = 3600 / elapsed seconds, where 3600 is the number of seconds in one hour. So if you cross a one-mile section in 60 seconds, your speed is 3600/60 = 60 MPH. If you do it in 30 seconds, it's 120 MPH. The tachymeter bezel is simply a pre-printed lookup table of this formula.

Can a tachymeter measure distance?

Yes, if you know the speed. Drive at a constant known speed, time one full chronograph minute, and the number on the tachymeter bezel where the hand points tells you the number of units (miles or km) covered in that interval. It is less commonly used than the speed function, but it is the same scale.

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Tachymeter Calculator

Last updated: April 2026 · 3 min read

Enter the chronograph elapsed time for a known distance. The calculator returns speed using the same formula as the tachymeter bezel on your chronograph watch.

Tool

Speed from Elapsed Time

Elapsed seconds

Distance unit

The tachymeter formula: speed = 3600 / elapsed seconds (for a 1-unit distance). Works for any unit — just make sure distance matches.

How to read the bezel on your chronograph

1. Line up the start. Press the top pusher (start/stop) the instant you cross the start of a known distance — a mile marker on the highway, a kilometer post.
2. Stop at the finish. Press the top pusher again when you cross the end.
3. Read the bezel. Wherever the big chrono second hand has landed, look at the number on the outer tachymeter scale — that is your average speed over the distance.
4. Reset. Press the bottom pusher to zero the chrono for the next measurement.

The scale usually reads from about 500 down to 60. Anything slower than 60 (more than a full revolution of the second hand) won't fit on a single rotation.

Tachymeter Calculator

Speed from Elapsed Time

How to read the bezel on your chronograph

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