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A chronograph scale converts the time measured by a watch’s stopwatch function into another reading. Depending on the scale, that can be average speed over a known distance, distance to an event you can both see and hear, or heart rate from a counted number of beats. The scale’s label and calibration tell you how to use it; its position on the dial alone does not.
What a chronograph scale does
A chronograph is a watch with a stopwatch function. Its pushers start, stop and reset the timing mechanism; the chronograph hand shows elapsed time. A scale on the dial or bezel interprets that elapsed interval as a different quantity. In mechanical chronographs, operating the controls engages or disengages a coupling clutch; the chronograph may be integrated into the movement or added as a module. The Foundation Haute Horlogerie explains the chronograph operating principle.
The scale is not a separate sensor. It relies on a known distance, the delay between a visible and audible event, or a fixed count of beats. The result is only as useful as the assumptions and calibration behind that measurement.
How to read the three common chronograph scales
| Scale | What you time | What it indicates | What to check |
|---|---|---|---|
| Tachymeter | Travel over a known distance | Average speed per hour in matching units | Distance unit and the model’s usable range |
| Telemeter | Delay between seeing and hearing an event | Approximate distance to the event | Whether the scale is marked in kilometres, miles or another unit |
| Pulsometer | A specified number of heartbeats | Heart rate, usually beats per minute | The beat count printed on the scale or specified in the manual |
Tachymeter: average speed over a known distance
A tachymeter scale converts the time taken to cover a known distance into a speed per hour. To use one, start the chronograph at the start of the measured distance and stop it at the end. Read the scale where the central chronograph seconds hand points. For example, on a scale calibrated for kilometres, the reading represents kilometres per hour; a mile-based measurement gives miles per hour.
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TAG Heuer’s guide describes timing 1 kilometre or 1 mile and says its procedure is for speeds above 60 km/h or 60 mph, depending on the model. Follow the scale and instructions for the specific watch rather than assuming every tachymeter has the same range. Read TAG Heuer’s tachymeter guide.
This is average speed across the measured distance, not a live or instantaneous speed reading. If the distance is not known, the tachymeter cannot produce a meaningful speed.
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Telemeter: approximate distance from a visible and audible event
A telemeter estimates distance by timing the gap between seeing an event and hearing its sound. Start the chronograph when you see the event; stop it when you hear it. The hand indicates the distance on the telemeter scale. Lightning and thunder are a familiar example: the visible flash comes first, and the thunder arrives later.
The scale’s units depend on its calibration. Hamilton’s instructions show a kilometre reading, while Tissot describes an outer telemeter scale for an event seen before it is heard. Consult Hamilton’s manuals and Tissot’s Telemeter 1938 description for their respective examples. Treat the result as approximate: it depends on a clear event and on correctly starting and stopping the chronograph.
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Pulsometer: heart rate from a fixed beat count
A pulsometer converts the time taken to count a specified number of heartbeats into beats per minute. The required count is set by the scale, so check its marking or the watch manual before starting; do not assume every pulsometer uses the same count.
Hamilton documents a base-30 procedure: start the chronograph, count to the 30th beat, stop, and read the beats-per-minute value shown by the hand. Its example gives 75 beats per minute. The Foundation Haute Horlogerie notes that pulsometer scales are commonly graduated for counts of 30, 20 or 15 beats. See Hamilton’s manual instructions and the Foundation Haute Horlogerie’s chronograph entry.
Quick Recap
How to identify the right scale on your watch
- Look for a printed name and units. Check the dial and bezel for labels such as “tachymeter,” “telemeter” or “pulsometer,” and note any units or count markings.
- Check the manual for the exact model. The scale’s placement and appearance are not enough to identify its purpose or operating range. TAG Heuer explicitly qualifies its tachymeter procedure by model.
- Separate overlapping scales. One watch may carry several scales. Tissot describes the Telemeter 1938 as having a central tachymeter, a minutes scale and an outer telemeter. Use the label and manual to match the intended hand and scale.
- Confirm the input the scale requires. A tachymeter needs a known distance; a telemeter needs a visible event followed by its sound; a pulsometer needs a fixed beat count. If that input is missing, the reading is not reliable.
What these scales cannot tell you
- A tachymeter does not report instantaneous speed; it converts elapsed time over a known distance into an average.
- A telemeter gives an approximate distance based on the timed visible-to-audible delay, not a direct measurement by a sensor.
- A pulsometer’s reading depends on using the count its scale specifies.
- Not every model uses the same calibration or procedure. The available operating guidance does not establish a universal method for asthmometer or slide-rule scales, so use the individual watch’s manual for those.
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