All You Need to Know About Chronographs

The chronograph is, without doubt, one of the most popular complications. It’s also one of the complications that can be used on a daily basis, however, what most people do not realise, is that the chronograph mechanism is among the most complex mechanisms to design and manufacture. For horology connoisseurs, there aren’t many experiences that are as rewarding as admiring the intricacies of a fine manual wind column-wheel chronograph. Here is everything you need to know about chronographs – An introduction to ‘time writers’ – from chronograph scales and flyback chronograph through split-second chronographs, foudroyante, column-wheel versus cams, horizontal versus vertical clutch, and integrated versus modular chronographs.

The origins

Chronograph can be directly translated from its Greek origins, a chronograph writes time (chronos=time, graphein=to write). However, chronographs actually allow us to display elapsed time intervals, and therefore should actually be called chronoscopes. The word ‘chronograph’ was invented by Nicolas Mathieu Rieussec, a watchmaker for the French King Louis XVIII. His invention actually writes time, as it inks measured times intervals on a rotating dial. However, timekeepers allowing to measure time intervals predate Rieussec. As early as 1776, Pouzait manufactured watches whose second hand could be stopped and restarted (not reset though).

The Louis Moinet ‘compteur de tierces’ pocket watch was discovered in 2013 and is remarkable. According to the markings on the case, it was made in 1815-1816. Designed to time the passage of stars, it measures events to the 60^th of a second with start, stop and reset functions. To reach this impressive precision its balance wheel beats at an impressive 216,000 vibrations per hour. Mind you, the average ‘normal’ mechanical movement these days beats at 28,800 vibrations per hour. The central hand indicates the sixtieth of a second; the second, minutes and hours are recorded on separate subdials. The Moinet creation was endowed with a start, stop and reset function. 

Until the 1930s, chronographs featured a single pusher to trigger the start-stop-reset functions always in the same sequence – a construction known as Mono-Pusher. The introduction of a second pusher allowed it to be stopped and restarted without the need to reset. There again, this function was already found in Moinet’s revolutionary ‘compteur de tierce’ with its two pushers.

Over the years, several mechanisms were invented to enhance their precision and improve chronographs. The Austrian chronometer maker Winnerl designed a split second mechanism in 1838 with a heart-shaped cam. At the beginning of the 20^th century, the sizes of chronographs were reduced to be fitted into wristwatches. Watchmakers also developed less expensive and simpler chronograph movements, in particular, with the invention of cams, to eventually replace the complex, high-end column-wheels to command chronograph functions. Surprisingly, the first automatic chronographs didn’t appear till the late 1960s, when three rivalling projects were competing in a true race to present the first automatic chronograph, which they did in early 1969: Zenith (with the famous El Primero movement – integrated, column-wheel, high-beat movement), a Heuer-Breitling-Büren partnership (with the Chronomatic – modular movement based on a micro-rotor calibre with module on the movement side) and, somehow more discretely, Seiko (with the ref.6139 – integrated, vertical clutch, column wheel).

Chronograph scales

Several scales might be indicated on chronographs. Among the most frequent ones, tachymeters, pulsometers and telemeters provide additional functions, while also giving them that “special touch”.

Tachymeter Scales allow the measurement of speed. To do so, the user starts and then stops the chronograph at a given marker, of a certain distance (in general one kilometre or one mile). The chronograph second hand indicates the corresponding speed on the scale.

Pulsometers, The so-called doctor’s watches, are chronographs which feature a scale allowing a simple and reliable rapid heart rate reading. The doctor starts the chronograph, counts a determined number of pulsations (usually it is calibrated for 15 or 30), stops the chronograph to read the patient’s pulse per minute on the pulsometer scale.

Telemeters allows the measuring of distance to an event, for instance, artillery firing or lightning, which can be seen and heard, using the difference between the speed of light and of sound. The chronograph is started when the event is seen and stopped when it is heard. The chronograph seconds hand indicates the distance from the event on the telemetric scale.

Fly-back

Also known as ‘retour-en-vol’ in French, flyback chronographs can be returned to zero and restarted instantly with only a single push of a button. Appreciated by pilots for the time it saves, this function allows beginning a new timing session quickly without the need of pressing pushers three times in succession to stop, reset and start the chronograph.

Split-second chronograph (Rattrapante in French or Doppelchronograph in German)

A split-second chronograph features 2 superimposed second-hands which time 2 events of different lengths simultaneously. One hand (the Rattrapante) can be stopped to read an intermediate time while the other one (the trotteuse) keeps running. A second push on the Rattrapante pusher will allow the stopped hand to catch up with the moving hand.

Split-seconds mechanisms are among the most complex to design and manufacture. Usually, a rattrapante wheel works in unison with the chronograph centre wheel, the heart-shaped cam ensures the chronograph and rattrapante hands are in perfect harmony. The rattrapante wheel is stopped by a clamp closed by the second column-wheel. Watchmakers have designed isolator systems, the purpose of which is to prevent friction which in turn would cause amplitude losses when the rattrapante is stopped. Pressing the rattrapante push-piece again, the clamp opens releasing the rattrapante wheel. The isolator is released and thanks to the heart-shaped cam, the two hands are superimposed again.

Foudroyante

A chronograph with foudroyante allows measurement of fractions of a second. Usually, the foudroyante hands completed one revolution per seconds. Traditionally, these are measured on a subdial and show fourth, fifth, sixth or eighth of a second (depending on the beat rate of the movement).

The foudroyante hand traditionally takes its energy from the main barrel, but some watchmakers, given its energy consumption, have developed systems with a separate barrel to power the chronograph and foudroyante such as the Jaeger-Lecoultre Duomètre à chronographe with its dual-wheel train regulated by the same oscillator.

Column wheel Vs. Cam

The traditional system to command the start, stop and reset functions of the chronograph is the column wheel. As the column-wheel rotates by increments when the chronograph pushers are pressed, the chronograph parts are driven by levers that fall into and out of the spaces between the teeth.

A column-wheel and its characteristic architecture (left). The splendid Montblanc Minerva M16.19 chronograph movement and its column-wheel (right).

A simpler, cost-effective solution which is much easier to produce, assemble and service is based on a cam system. Pushes on the chronograph buttons move the cam to start, stop or reset the chronograph. If cam-actuated chronographs also prove to be robust, reliable and efficient the column-wheel chronograph are regarded as a more noble, elegant and traditional solution.

Horizontal vs. vertical clutch

The usual working principle of chronographs is based on a connection between the chronograph and the regular timekeeping gear trains. This coupling was traditionally done horizontally thanks to a gear which is free to pivot and allows the connection of the gear train to the chronograph centre wheel. A solution invented and patented by Tag Heuer in 1887, the oscillating pinion, allows the pinion which is constantly engaged with the second wheel of the movement to couple or de-couple with the chronograph wheel train. When the oscillating pinion is engaged, the chronograph is running.

As its name indicates, with a vertical clutch, the coupling of the chronograph mechanism is positioned vertically and by friction, similar to the systems found in automobiles. While horizontal clutches are aesthetically appealing, simple and thinner mechanisms, the theoretical advantages of vertical clutch chronographs is that there are no teeth to engage or disengage, a principle that may cause the jump of the chronograph second hand when the teeth mesh. In addition, the teeth may wear overtime with horizontal clutches.

Integrated vs. modular chronographs

There are fundamentally only two types of chronographs designs: modular or integrated. The integrated chronograph is a movement that was designed to be a chronograph from its inception. All the chronograph functions are built-in which is the most elegant and appropriate solution.

On the other hand, a modular chronograph is using a base calibre on which a chronograph module is added. This allows much flexibility and offers the possibility to take advantage of economies of scale from the production of the base calibre. Nestled in the Vallée de Joux, Dubois-Dépraz designs and manufactures additional movements for some of the greatest names in the industry and has a wealth of expertise in the production of chronograph modules.

Other posts in “A Technical Perspective“: Escapements, Jewel Bearings, Moon Phase Watches, Travel Watches and Haute Horlogerie Finishing.

article edited 20 March 2020.