The basic function of any watch, with very few exceptions, is to tell the time. Whether with two hands, three, or digitally, the end result is the same. But many watches show much more on the dial. Most use a type of calibrated scale that imparts a measurement of some sort beyond the basic hours, minutes and seconds.
It is tempting to consider these scales mere decoration as they can add significantly to the visual impact of a watch. But it is nice to have an idea of what they show and how they work, even if we never use them as intended. Below, we’ll consider the most common dial scales found on wristwatches.
Between the wars, it became popular for a watch to have several scales on its dial. These dials were versatile, but often difficult to read.
One such scale was the telemeter. The word itself gives away the function, its components coming from the Greek têle, meaning “far”, and metron, meaning “measure” so a way of measuring distance, specifically range-finding.
The gist of it is to press the top pusher once when you see the muzzle flash or smoke of enemy gunfire and press it again when you hear the report. The distance of the gun can then be read from the telemeter scale and the range set for your own artillery to reply. This scale became less popular after World War II, but appears on the occasional watch today.
The primary usage of the tachymeter is to measure speed over a fixed distance. The pusher is pushed once at a specific point and again once a second reference point is reached, such as the mile markers on a highway. If you’re in Germany feel free to measure the kilometer markers on an Autobahn: the tachymeter is agnostic to the units being measured.
This is explicit on the bezel of most Rolex Daytonas, marked with “units per hour” text. That didn’t stop some manufacturers thinking that the markings were specifically kilometers and releasing watches with the measurements “converted” to miles. This doesn’t work as the converted markings don’t correlate to the actual tachymeter readings, as they are universal.
These scales can show a different range of numbers, but the position of the numbers is always the same, and this is what is key to the tachymeter being a universal scale.
For example, that Daytona shows a range from 400 to 60. The scale decreases because the longer it takes, the lower the number of units being measured. Let’s take that flying mile again. If you complete it in 30 seconds, then the tachy reading is 120, so you were running at a speed of 120 mph. Take 60 seconds and the scale tells us you were doing (a fairly self-explanatory) 60 mph.
Other tachymeter scales run from 200 to 50, which at first glance appears entirely different, but remember it’s the position that matters. That first reading of 200 is shown at 18 seconds, which is exactly the same position as 200 is shown on our Daytona’s 400 to 60 scale. That 50 reading is at 72 seconds, i.e. more than one full revolution of the second hand. It’s not explicit on the Daytona’s scale, but if you were to stop its second hand at 72 seconds, it too means 50 units per hour.
Some watches, like the Eberhard Contograf, have a “full” 1000 to 60 tachymeter scale and also incorporate a 50 marking in contrasting colors at the 72 seconds mark.
A less common scale, perhaps because of its lack of sporting connotations, is the decimal scale, where each minute is divided into 100 portions. This is used more for industrial and scientific timings than for racing.
Expressing a timing in this decimal fashion allows you to more readily perform any series of arithmetical operations on it, converting back to hours, minutes and seconds only at the end.
As arguably a less glamorous scale than its tachymeter partner, this was often only to special order. Nonetheless, it appeared on sporting watches like the Heuer Carrera and Omega Speedmaster and can still be found now on watches like Breitling’s Chronomat, where it features alongside a tachymeter scale.
Another scale with a quite pragmatic use is the pulsometer. Just about every Swiss maker of long standing has produced these at some point in their history, from a non-chronograph Swatch all the way up to Patek Phillippe and Vacheron Constantin.
The scale works by counting out a specific number of pulses, often fifteen, and then referring to the marked number on the scale to derive the pulse rate. The scales are usually marked with the base number of pulses to count.
The average pulse rate for an adult is 60-100, so watches with combined scales often only show the pulsometer scale for fifteen seconds, not expecting to need to measure pulse rates below sixty. Michael Schumacher at his peak famously had a resting heart rate in the mid 30s, but during races an F1 driver’s pulse rate rises to over 150.
There are many other types of scales on watches, of course. From the navigation aids on pilot’s watches like Breitling’s Navitimer, through slide-rule conversions on Heuer’s vintage Calculator, to simple power reserves, the information that can be shown on a watch dial is incredibly diverse.
With the advent of more advanced medical monitoring, the pulsometer is now very rare and the telemeter too has been largely superceded. While I can’t see any new scale coming along to usurp the tachymeter’s number-one watch dial position, it is interesting to see continued variety on the market. I hope you now can put whatever scales you own to good use.