CHRONOGRAPHS
Time and sport are invariably linked. The relationship is so obvious that it often goes unnoticed. Over the years, various types of timers have been used to assess athletes' performance. The first chronographs, used in horse racing, could be considered the forerunners of the modern video assistant referee. Since then, ever more accurate and sophisticated chronographs have been developed. Reading their scales, as well as understanding how they work and their mechanics, remains an enigma for many, a mystery we set out to unravel.
SIMPLE WATCHES, CHRONOGRAPHS AND CHRONOMETERS
A simple watch shows the hours, minutes and seconds, but being able to indicate the time is significantly different from being able to count it. In the world of sport there are specific devices called chronometers, which are used to measure the time elapsed in competitions.
It is important to distinguish between sports timers, wrongly referred to as chronometers, and watchmaking chronometers.
In watchmaking, a chronometer is a watch whose accuracy has been individually certified by an officially recognised body, such as the COSC (Contrôle Officiel Suisse des Chronomètres). It should not be confused with the chronometers used in sporting competitions. These devices, commonly called chronometers in sport, are in fact chronographs.
Watchmaking chronometers
Sports timer, frequently referred to as a chronometer
But what, after all, defines a chronograph?
A chronograph is a watch equipped with an additional time-counting function. The term “chronograph” derives from “chrono” (time) and “graph” (writing), literally meaning “time writer”, because these devices originally recorded time in written form.
THE ORIGIN
The chronograph as we know it today emerged from the innovations of several watchmakers throughout history. In 1720, George Graham introduced the first device capable of measuring intervals of time independently, based on stopping and restarting a pendulum. Although in 1822 Rieussec gave the name chronograph to his invention, which actually marked the time with a drop of ink on the dial, it is widely accepted that Louis Moinet's “compteur de tierces”, created in 1816, deserves the title of the first chronograph in history.
This innovative mechanism ran at a frequency of 216,000 vibrations per hour, equivalent to 30 Hz, making it possible to divide the second into sixty fractions, all driven by a foliot oscillator. By way of comparison, a common watch today runs at a frequency of 14,400 oscillations per hour, or 4 Hz. These advances were some of the most significant early contributions to the evolution of the chronograph. However, there are other, less celebrated inventors, such as Adolphe Nicole, who also played crucial roles in perfecting this mechanism, notably by creating the first system that allowed the hand to return to zero.
SCALES AND DIVISIONS
The vast majority of chronographs are able to measure hours, minutes and seconds, using three hands and scales with standard divisions to do so. However, in addition to these traditional scales, other more specialised ones are often added, such as the tachymeter and telemeter scales. Watches fitted with such scales are named after the scale in question and are called, for example, tachymeters or telemeters. These are indeed the most common scales on chronographs, but there are other, rarer ones, such as pulsometer, asthmometer or decimal scales.
Angelus telemeter, Angelus pulsometer with asthmometer scale and Omega tachymeter
Tachymeters are used to calculate the speed of an object based on times marked over predefined intervals. To determine the speed of a car covering the distance between two markers 1 km apart, simply start the chronograph when passing the first marker and stop it when passing the second. The chronograph hand will then indicate the speed at which the vehicle travelled. For example, if the hand stops at the 30-second mark on the standard scale, a close look at the tachymeter scale will reveal that the corresponding speed is 120 km/h. If the car took 30 seconds to cover 1 km, that means it travelled at 2 km per minute, which equals 120 km/h.
Telemeters, on the other hand, make it possible to measure the speed at which sound travels, about 330.7 m/s, or approximately 1 km in 3 seconds. If, for example, we start the chronograph on seeing a flash of lightning and stop it on hearing the thunder, the hand will indicate how far away the storm is. This scale was widely used in wartime to measure the distance to the enemy's guns.
In some chronographs, especially the more complicated ones such as the famous Breitling Navitimer, slide rules are built in, making it possible to carry out a series of additional calculations, such as fuel consumption or flight time.
FUNCTIONAL ASPECTS
Chronographs have three basic functions: start, stop and return to zero, and these functions are normally operated by two pushers. So if there are three functions for two pushers, one of them must necessarily perform two functions. One of the pushers controls the start and the stop: when it is pressed, the chronograph hand begins to move every fifth of a second, in a watch running at 18,000 vph, and completes one revolution every minute. Pressing the same pusher again stops the chronograph system. During this stop, a click on the second pusher returns the chronograph hand to its starting position. This is the most common way a chronograph works, but there are several options, such as single-pusher chronographs, monopoussoir, or monopusher, which today allow all functions to be performed except restarting after a stop. After the stop, using only one pusher, it is only possible to perform one function and, naturally, that function has to be the return to zero and not the restart of the count.
Chronographs are normally categorised according to functional aspects or aspects of mechanical construction. The functional aspects take into account the way the counts are displayed, which results from the number of counters, hands or pushers.
A simple chronograph has only one independent central hand, called the chronograph hand. The whole mechanism is controlled by a single pusher, which starts, stops and returns to zero. This type of mechanism has the drawback of only counting up to 60 minutes. Examples are the Omega Chronostop, the Singer Flytrack, or the parking-meter watches of the 1970s, which counted the minutes of parking time elapsed.
A counter chronograph adds minute counters, and sometimes hour counters, to the simple one. This is the most common system. The counters are subdials with their own scales and hands, normally placed at 3 and 6 o'clock, which makes it possible to add small seconds at 9 o'clock, thus creating some symmetry.
A. Lange & Söhne 1815 Rattrapante 
A. Lange & Söhne 1815 Rattrapante
A. Lange & Söhne 1815 Rattrapante
The split-seconds chronographs, rattrapante or splitsecond, have more complex movements, with two superimposed central hands: one is the chronograph hand, the same as in the previous types, and the other is the split-seconds hand, which makes it possible to take intermediate timings. These watches have two pushers, like the previous ones. The first starts and stops the mechanism and the second returns it to zero. In addition to these two pushers, there is a third which, with a single click, stops the split-seconds hand and, with another, sends it to rejoin the chronograph hand, both running together from that moment on. The Lange & Söhne Triple Split Ref. 424.038F is a great example of a rattrapante, especially because it was followed by two technological marvels, the double and triple split-seconds chronographs, which are also flyback chronographs, all using three pushers and 10 hands.
In the early days of aviation some pilots used a very particular type of chronograph that made it easier to calculate distances and speeds, without the need for the usual separate stop and return to zero. These are the flyback chronographs, retour-en-vol, or flyback. Their operation is very simple: these watches start running with the start/stop pusher, a second click on the start/stop pusher stops the chronograph hand and a click on the second pusher returns it to zero, as in all the others. Nothing new so far. The difference is that, once the chronograph hand has started, the second pusher returns it to zero and it then restarts automatically. In other words, after a quick reading, one click starts a new count automatically. Flyback chronographs are common models in several brands.
All these chronographs count down to the second at most, but what if a second needs to be divided into several parts? In that case we need a chronograph with a lightning seconds hand; the most commonly used terms are foudroyante in French or split-seconds in English, while the Italians call it “diavoletto”, little devil.
This is in fact quite an old technology: the compteur de tierces by Louis Moinet, regarded as the first chronograph, has a lightning seconds hand. Whenever the counts have divisions longer than a second and shorter than a minute, they are said to be chronographs with a semi-lightning hand. The Zenith El Primero Striking 10th, for example, has a central hand that makes 6 revolutions per minute, which allows 1/10 of a second to be counted, or the Jaeger-LeCoultre Duomètre à Quantième Lunaire which makes the same count but on a dedicated counter.
Zenith El Primero Striking 10th and Jaeger-LeCoultre Duomètre à Quantième Lunaire
This mechanism is possible thanks to the different frequencies: a movement at 14,400 vph, for example, makes 4 oscillations per second, which allows a measurement of 1/4 of a second. The Zenith El Primero, which runs at 36,000 vph, allows divisions of 1/10 of a second and, with the same frequency, the TAG Heuer Calibre 360 counts 1/100 of a second. These chronographs with lightning seconds hands consume a great deal of energy, and while the F. P. Journe Centigraphe Souverain effectively relies on a single barrel, the Jaeger-LeCoultre Duomètre à Chronographe soberly uses two barrels to power the whole mechanism. An ingenious way of dividing a second into parts can be seen in the Longines Nonius, the TAG Heuer Grand Carrera 36 RS Caliper, or the Alain Silberstein iKrono.
TAG Heuer Calibre 360 | Longines Nonius | Alain Silberstein iKrono
All these models make use of a vernier (nonius), an invention of the celebrated Portuguese mathematician Pedro Nunes. In the examples of the Longines Nonius and the iKrono, the vernier is built directly into the chronograph hand. Interpreting the measurements is not simple: it requires understanding which mark on the vernier scale lines up with the chronograph scale and counting all the preceding marks, thus making it possible to determine tenths of a second accurately.
The way the minute counter hand moves also makes it possible to distinguish between different types of chronograph. There are three patterns of movement for these hands: they can be continuous, gliding steadily; instantaneous, moving in one abrupt jump; or semi-instantaneous, gliding half the way before making a jump. The most common are the semi-instantaneous ones, in which the minute counter hand begins to move at 58 seconds and travels half the way to the next minute over the following 2 seconds; once those two seconds are over, it makes a final jump to mark the change of minute. This mechanism can be clearly seen in a video recorded on a mobile phone in slow-motion mode. Chronographs that include hour counters are found less often and generally have minute counters that operate in semi-instantaneous mode.
ASPECTS OF MECHANICAL CONSTRUCTION
Almost all chronographs have a driving wheel (1), fixed on the seconds arbor and meshing with the coupling wheel (2); the chronograph hand starts to move when the chronograph wheel (3) comes into contact with the coupling wheel. In the case of the famous ETA 7750, the driving wheel was replaced by an oscillating pinion.
Omega calibre 321 movement, highlighting the
driving wheel (1), coupling wheel (2), chronograph wheel (3) and column wheel (4)
Two possible types of control are involved in this process: a cam mechanism or a column wheel.
Cam mechanism | Column wheel
Eccentrics or cams are parts whose axis of rotation is not centred, so that when they are pressed they rotate until they reach a single position.
In addition to the cam system, there are other eccentrics called hearts because of their shape. These hearts play an important role in the return to zero.
Cams identified in a chronograph movement
Both the coupling wheel and the chronograph wheel have triangular teeth, but those of the chronograph wheel are more numerous and more closely spaced, which reduces the jump the chronograph hand makes when the teeth of the two wheels mesh.
Driving wheel on the left | coupling wheel at the top (triangular teeth) | chronograph wheel on the right (triangular teeth)
Control by column wheels gives a feeling of greater precision when using the pushers; however, assembling it demands very tight tolerances and it is often considered that the production costs outweigh the benefits brought by the increase in precision. The transition from the column wheel to other solutions was not simple and resulted in several patents, since the cycle of functions (start, stop and reset) is more easily achieved with a part that turns on itself, like the column wheel, than with parts that only make partial rotations.
Column wheel
The column wheel is easy to identify because it resembles a round castle with battlements, and it is visible in some high-quality mechanisms, although it is often hidden in Patek Philippe chronographs.
Patek Philippe Ref. 5172 with hidden column wheel
The operation of the column wheel begins with a click on the start/stop pusher. By pressing this pusher we move a lever called the operating lever, with a hook at its tip that engages the base of the column wheel, which consists of a wheel with Breguet teeth, that is, saw-shaped teeth. This hook turns the base and, consequently, the whole column wheel: the base rotates and, being solid with it, so does the entire column wheel, which always turns in the same direction and never reverses. This process brings the beak of the coupling lever to sit between two of the columns of the column wheel and so pushes the coupling wheel against the driving wheel, which starts the chronograph system. The stop occurs when the hook causes a second rotation of the column wheel, and with it a new position of the beak of the coupling lever, with the coupling wheel consequently moving away from the driving wheel or oscillating pinion. The return to zero is triggered by a second lever which has a hammer at one end and two tips at the other; the hammer enters between the columns of the column wheel and, when this happens, each tip turns an eccentric, coming to rest on its flattest part. The rotation of the two eccentrics results in the hands of the chronograph counters returning to zero.
Besides the chronograph control, another distinguishing element is the clutch system. In a car, a clutch transmits rotation from the engine to the gears of the gearbox. In a watch, the clutch transmits the rotation of the mainspring and barrel to the gears of the chronograph system. There are horizontal clutches and other, more modern ones, the vertical clutches. Horizontal clutches move the coupling wheel until its teeth mesh with the teeth of the chronograph wheel.
Vertical clutch of the Rolex calibre 4130 that powers the Rolex Daytona
Vertical clutch of the Caliber 9SC5 that powers the Grand Seiko Tentagraph
In vertical clutches the motion is transmitted by friction, with the driving wheel and the chronograph wheel stacked concentrically and sharing the same axis.
Detail of the Rolex calibre 4130
It is as if the chronograph wheel were a vinyl record dropping onto the driving wheel, the platter of the turntable. A good example of a movement with a vertical clutch is the calibre 4130 that powers the most recent Rolex Daytonas. This clutch system allows a more precise start of the chronograph hand, since there is no initial jump caused by the meshing of the teeth. In practice, however, these differences are very hard to notice.
SPECIAL CHRONOGRAPHS
The battle to create the first automatic chronograph in 1969 is an often-told story, involving the Zenith El Primero, the Seiko 6139 and the consortium formed by Breitling, Buren, Hamilton, Heuer and Dubois-Depraz. This innovation, the automatic chronograph, was an important milestone for its time, especially considering the limited resources available.
MB&F Sequential EVO
Over the more than fifty years that followed, master watchmakers have never stopped innovating; here are some of the most inventive examples. The MB&F Sequential EVO, with its Twinverter system, designed by Stephen McDonnell, introduced a series of remarkable innovations, consisting of two independent but interlinked chronographs in the same watch.
This configuration allows for a chronograph hand and a split-seconds hand, both operating autonomously. The mechanism, governed by two column wheels, has 4 counters: two of 60 seconds and two of 30 minutes each.
It is operated by five pushers: each of the chronographs is operated by two pushers and the fifth activates the Twinverter function. In practice, this works as follows: if both chronographs are stopped, they are started simultaneously; if both are running, they are stopped together; if one is running and the other is not, pressing the fifth pusher (the Twinverter pusher) at 9 o'clock stops the one that is running and starts the one that is stopped. This chronograph also includes a vertical clutch that works not by friction but by meshing with two wheels simultaneously. As a result, operating the chronograph does not affect the amplitude of the balance.
Grönefeld 1941 Grönograaf
Another significant innovation came with the Grönefeld 1941 Grönograaf, notable for its system that softens the chronograph hand's return to zero. This motion is usually abrupt and causes wear to several parts, and can even lead to the hands coming loose.
AgenGraphe AGH-6361
The solution adopted uses two gold counterweights, which employ centrifugal force to soften this process, in a way similar to that found in minute repeaters, making it a true spectacle of watchmaking mechanics visible through the dial. Observing the mechanism reveals other innovations, such as levers fitted with ruby hammers.
AgenGraphe AGH-6361: Singer Reimagined Track 01, Moser Streamliner and Fabergé Visionnaire
The AgenGraphe AGH-6361, produced by AgenGraphe and used in the Singer Reimagined Track 01, the Moser Streamliner (modified into the HMC 902) and the Fabergé Visionnaire, ranks among the most innovative chronographs of recent times.
What immediately stands out in this mechanism is its unusual doughnut-shaped configuration, with the chronograph counters (seconds, minutes and hours) all concentrated in the centre, instead of being distributed around the dial as is usual. With instantaneous indication of hours and minutes, a column wheel and a vertical clutch, this automatic mechanism has its rotor located beneath the dial, above the movement. Since the centre is devoted to the three counters, in the case of the Singer the hours and minutes are displayed on rotating rings at the periphery; the outer ring shows the hours and the inner one the minutes, with the correct time indicated by a fixed pointer at 6 o'clock.
This is a technical watchmaking article aimed at enthusiasts and collectors; if you have any questions, please get in touch with us or leave a comment in the message box below.
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