Scale

On a dial or bezel, a scale is a functional graduation that transforms the time measured by the chronograph into another quantity: speed, distance, heart rate, respiratory rate. It is not decoration. It is a calculating instrument built into the crystal or printed on the dial.

The tachometric scale is the most widespread. It measures average speed over a fixed distance, usually one kilometer: you start the chronograph at the first reference point, stop it at the second, and the hand directly indicates km/h on the graduation. The telemeric scale works differently: it exploits the difference in speed between light and sound. You start at the flash, stop at the thunder, and read the distance in kilometers. It was a practical tool for aviators and artillerymen; today it is a philological element in sports chronographs of traditional design.

The pulsometric scale counts heartbeats over 15 or 30 seconds and projects them to 60, indicating beats per minute. It is the signature of medical chronographs from the 1940s and 1950s, often paired with a respiration scale for breathing rate. I have restored several Longines and Universal Genève watches with both scales on the dial: the precision of the graduation is rarely appreciated as much as it deserves.

The decimal scale, used in industrial contexts, divides the minute into one hundred units rather than sixty. It allowed a workshop foreman to read directly the percentage of the hour elapsed, without conversions. The Gallet Multichron Decimal is the most cited example.

Scales can be found in different positions: on the dial in the outer track, on the rotating bezel, on the rehaut, or even arched under an opening of the tourbillon. The snailed scale — engraved in a spiral, often in double spiral — is a rare variant that replicates the ultra-flat dials of the 1930s, where space was precious and readability was solved through geometry. A 24-hour GMT scale, on the bezel or dial, allows you to read a second time zone; if the bezel is bidirectional, you can also track a third. The no-decompression scale on the Doxa Sub is a case apart: it does not measure a physical quantity, but signals safe immersion times to avoid decompression sickness, with logic closer to a table than to a calculating scale.

From the bench, I would add a distinction that magazine notes tend to confuse: scale and index are not the same thing. Indices are fixed hour references; the scale is a graduated progression designed for a specific measuring function. When both are absent, the watch makes another aesthetic and functional choice — legitimate, but different.