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1. General Information

The Chronograph is a device designed to accurately measure the time elapsed between two events. Its history is marked by the influence of several visionary Horologists (watchmakers) who, through their inventions, laid the foundations of this complex mechanism as we know it today.

2. Chronograph or Chronometer?

Confusion is sometimes made between these two terms. The Chronograph refers to a mechanism for measuring short periods of Time, operating independently of the watch’s Time Display. The Chronometer, on the other hand, refers to a highly precise watch once certified by chronometric observatories and nowadays governed by the ISO 3159 international standard

3. History and Etymology

3.1 Etymology of the word “Chronograph”

The term “chronograph” comes from ancient Greek, “chronos” (χρόνος), meaning “time,” and “graphein” (γράφειν), meaning “to write.” Literally, a chronograph is an instrument intended to “write” time. In its evolution, the inking chronograph, invented by Nicolas Rieussec in 1821, reinforced this meaning: the device marked the passing of time using an inking stylus, leaving a visible trace on a rotating disc. This innovative mechanism made Rieussec the pioneer of the chronograph as we know it today. Because of this, it would be more accurate today to speak of a “chronoscope.”

3.2 History of the Chronograph

Louis Moinet (1768-1853)
Louis Moinet, a brilliant French horologist, is recognized as one of the inventors of the chronograph, his thirds counter having been made a few years before Rieussec’s chronograph. In 1816, Moinet filed a patent for a chronograph capable of measuring durations with an unprecedented precision of 1/60 of a second. To achieve this, he created a Regulating organ oscillating at 30 Hz (compared to 3-5 Hz for a conventional modern watch). While one can imagine the impact on Lubrication, on the Power reserve and on the wear of components imposed by such a Frequency, Moinet’s work laid the foundations for precise time measurement in practical applications.

Nicolas Rieussec (1781-1866)

One of the founding moments in the history of the chronograph dates back to 1821, when Nicolas Rieussec, a French horologist, invented the inking chronograph. Rieussec, keen to address a specific need in horse racing, developed a mechanism in which a stylus, inked, left a visible mark on a rotating disc each time it was activated. This innovative device allowed him to precisely measure elapsed time, which had until then been difficult to measure with conventional clocks. Rieussec’s “inking chronograph” is thus the origin of the function known today as the “chronograph”. At this stage in the history of the chronograph, the mechanism only had a start and stop control, the “reset” function not yet existing and being carried out manually by exchanging the graduated cardboard disc placed on the Dial rotating part of the mechanism.

Frédérick-Louis Fatton (1812-1876)

He was a student of Abraham-Louis Breguet, who welcomed and encouraged his work, as he did with Rieussec’s, moreover. Fatton filed, in 1822, only a few months after Rieussec, the patent for a chronograph (inker) whose dial is fixed. Here, it is the Hand that is in motion and fed by an ink reservoir.

3.3 Authorship of the invention

It is difficult to attribute the authorship of the chronograph to a single horologist, as so many contributed jointly to its invention and development. An exhaustive list of the horologists who contributed to the development of the chronograph(s) is impossible, but we can still mention names such as John Arnold, Abraham-Louis Breguet, Joseph-Thaddeus Winnerl, Abraham-Louis Perrelet, or even Adolphe Nicole, who developed systems such as heart-piece reset to zero, the integration of an independent second into the Movement of the watch, the Monopusher chronograph, or the Split-seconds chronograph, for example.

From the ink used by Rieussec to mark time to Winnerl’s independent reset-to-zero mechanism, these inventors each played a major role in the evolution of horology and in the development of timing mechanisms that are both sophisticated and precise.

4. Integrated Chronograph or Additional Module?

The Chronograph is a short-time measuring mechanism that is added to the traditional mechanism of the watch intended to display the time. There are two ways of designing the construction of a Chronograph. The first consists of integrating the Chronograph mechanism into the Movement base right from its design. This type of construction means that the Movement will be used exclusively for watches equipped with a Chronograph. It is generally accepted that an integrated construction is more authentic and of better quality than an additional mechanism.

The second solution for producing a chronograph consists of using a traditional movement intended to display hours, minutes and seconds, and superimposing on it an additional mechanism (called a module) integrating all the components specific to the chronograph function. This solution minimizes development costs and offers great logistical flexibility, as a module can be assembled on different base movements and a base movement can receive modules of complications different.

5. Column wheel or shuttle (Cam)?

The various functions of the Chronograph (start, stop, reset, Split-seconds chronograph functions, etc.) are orchestrated by a Cam of which there are two types:

5.1 The column wheel

This is a circular Cam fitted with a ratchet toothing at its base and topped with a variable number of vertical pillars: the columns. With such a mechanism, each press on one or the other of the pushers makes the column wheel rotate (advance) by one step of its ratchet teeth. The coupling lever(s), hammer(s), and brake(s) have a finger that keeps them pressed against the circumference of the columns.

With each advance of the column wheel (pressure on a pusher), the fingers of the levers, hammers, and brakes will simultaneously be positioned on the circumference of the column or in the slot located between two columns, which allows the different chronograph components to be moved according to a perfectly defined order and amplitude of movement. By its construction, the column wheel rotates in only one direction.

5.2 The Shuttle

This is a Cam generally on two levels (two concentric and interconnected Cams superimposed), sometimes three, which orchestrates all the functions of the Chronograph. Unlike the column wheel, the shuttle performs a clockwise rotational movement when the start command is given and a counterclockwise movement when the stop command is given. The shuttle thus performs a back-and-forth movement, which gives it its name. The reset command moves the shuttle to a third position, which releases the Brake and activates the hammer(s).

6. Horizontal Coupling or Vertical Coupling?

The Chronograph draws its energy from the Movement base and is generally driven by the Fourth wheel (seconds wheel) of the movement. The Chronograph mechanism must therefore be coupled to the base Movement when it is running and uncoupled when it is stopped. Two Coupling methods exist:

6.1 Horizontal Coupling

The horizontal coupling was the only one used until the appearance of vertical couplings at the end of the 20^th century. With this type of mechanism, the pivot of the fourth wheel (seconds wheel) extends above the surface of its bridge. A crown wheel is driven onto it, turning at the same speed as the fourth wheel (seconds wheel) (generally 1 rpm). The coupling lever pivots around the axis of the fourth wheel (seconds wheel) and the crown wheel, and carries the coupling wheel (or chronograph intermediate wheel). The crown wheel and the coupling wheel are constantly driven by the fourth wheel (seconds wheel) regardless of the engaged function of the chronograph (start or stop). The coupling lever ends in a finger held in contact with the column wheel by the effect of the coupling lever’s spring.

By activating the “start” function via the dedicated pusher, the column wheel advances by one step and the Finger of the Coupling Lever / Rocker falls into the space located between two pillars of the column wheel. The Coupling Lever / Rocker thus pivots around its Axis and carries the Coupling wheel in a movement concentric to the edge-mounted wheel with which it remains engaged. At the end of this movement, the Coupling wheel comes into contact with the chronograph wheel and drives it. At the same time, the Brake is released, and the Chronograph starts. This construction is valued for its historical and authentic character. However, it has the drawback of a (limited) risk of imprecision when starting the measurement, due to the distance the Coupling wheel must travel. Moreover, since the Coupling wheel is constantly rotating, there can be a tiny offset between the position of the teeth of the Coupling wheel and those of the chronograph wheel at the moment they begin to mesh. It is these two imperfections of the system that led to the development of vertical Coupling chronographs.

6.2 Vertical Coupling

There are different designs ofvertical couplings. The general principle consists of superimposing the coupling wheel onto the chronograph’s intermediate wheel, or directly onto the chronograph wheel with which it moves concentrically. When the chronograph start is activated, the coupling wheel rises into contact with the chronograph’s intermediate wheel or the chronograph wheel, sliding along its axis while still being driven by the seconds wheel. Between the two wheels are placed the coupling pad and spring, which guarantee perfect and instantaneous driving of the chronograph wheel.

7. Counters and Scales

A chronograph displays, at minimum, the measurement of seconds. This is indicated by a hand, usually central, for more precise and easier reading. The seconds scale is generally subdivided into several divisions. These correspond to the Frequency of the Regulating organ of the watch. Thus, for example, the frequency of a regulating organ oscillating at 18,000 vph (i.e. 2.5 Hz) will have a chronograph hand that makes 5 jumps per second (1/20th of a second), whereas with a regulating organ oscillating at 5 Hz, the second will be divided into 10 jumps of the chronograph hand (accuracy to 1/10^th of a second).

The seconds is frequently complemented by a minute counter (totalizer). Although it can also be displayed at the center, the minute counter (Figure 1) generally appears on a Dial offset (off-center). At each minute, i.e., one revolution of the chronograph hand, the minute counter advances by one division. Minute counters are often graduated in increments of 30, 45 or 60 minutes.

Figure 1

Minute Counters

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Ce compteur de minutes est souvent complété par un compteur d’heures (Figure 2) disposant généralement de son propre cadran reporté et affichant une graduation sur 12 ou 24 heures.

Figure 2

Hour Counters

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The jump of the Display of minute and hour counters can be dragging, semi-instantaneous or instantaneous (Figure 3).

Figure 3

Different counter jumps

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8. Telemeter, tachymeter, pulsometer?

Various conversion scales, or even calculating rules, can be displayed concentrically to the graduation of the seconds of the Chronograph. These can be engraved or pad-printed on the Dial, on a flange or on a Bezel, fixed or rotating.

8.1 The Telemeter

It allows measuring a distance based on the speed of sound. Its use is essentially military. For example, to know the distance traveled by a shell that has just been fired. By starting the chronograph when the shell is seen exploding and stopping it when the sound of the explosion is heard. Thus, if there is a gap of 7.4 seconds, the shell will have exploded 2.5 km from its launch point. Due to the need to visualize the event (explosion) and perceive its sound (even at long distance), the telemeter has hardly any other uses, except to determine at what distance lightning has struck (Figure 4).

Figure 4

Telemeter

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8.2 The Tachymeter

This is a scale that allows, in turn, the measurement of a speed or a rate. Here again, a reference will be needed. For example, to calculate the speed of a vehicle, a distance reference is required (for example 1 km). Most highways have markers spaced exactly 1 km apart. By measuring the exact time it takes a car to cover 1 km (for example 21.5 s.), one can accurately determine its actual speed (167.4 km/h in our example).

One can also determine the hourly output of a machine by measuring the time it takes to manufacture a component. Thus, if the complete production cycle of a part lasts 12 seconds, the machine will produce 300 parts per hour (Figure 5).

Figure 5

Tachymeter

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8.3 The Pulsometer (pulsation scale)

Watches equipped with a pulsometer were once commonly referred to as “doctor’s watches”. In order to calculate a patient’s number of heart pulsations per minute, it is enough to measure the duration of a limited number of pulsations. For example, if the scale indicates a pulsometer for 30 pulsations, it is enough to measure the total duration of 30 pulsations to know the number per minute. This scale thus allowed doctors to save time when taking this measurement. (e.g.: 30 pulsations in 22.5 s give a heart rate of 80 pulsations per minute) (Figure 6).

Figure 6

Pulsometer (pulsation scale)

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10. CHRONOGRAPH “FLYBACK” (FLYBACK)

This mechanism was developed for the use of aircraft pilots so that they would not lose time between two time measurements related to managing their aircraft’s approach. When the Chronograph is engaged, a simple press on the Pusher reset function simultaneously and instantly performs the stop, reset and start functions, allowing you to switch to the next measurement with a single press.

12. MONOPUSHER CHRONOGRAPH

As its name suggests, all the controls of this type of chronograph are operated by a single pusher. The three stages of the chronograph (start, stop and reset) follow one another in a loop each time the pusher is pressed.