One of the most famous chronographs in history is the Omega Speedmaster worn by astronaut Jack Swigert on the near-disastrous flight of the Apollo 13. With the spacecraft embattled after one of its oxygen tanks exploded on April 13th, 1970, the crew had to shut down some of their systems to conserve power for their return journey to Earth. The retelling goes that the calm and collected astronauts then decided to use Swigert’s NASA-qualified Speedmaster to time a 14-second engine burn — one of several critical manoeuvres — for the purpose of correcting the angle of the spacecraft’s re-entry to Earth’s atmosphere. The correct burn time and angle would ensure the crew’s safe return to Earth; an inaccurate time would result in a too-sharp or too-flat angle, causing problems for the ship that would lead to their certain demise. As we know, the manoeuvres proved successful, culminating in a splashdown in the Pacific Ocean, where Swigert and his fellow astronauts Fred Haise and Jim Lovell were immediately picked up by the USS Iwo Jima and whisked off for health checks and an awards ceremony with President Nixon.
The “successful failure” of the Apollo 13 was, as Ron Howard’s 1995 movie puts it, the “finest hour” for the United States’ space agency — it was proof positive of the technical skills and mental tenacity of the NASA teams involved. But it was also the finest hour for the Omega Speedmaster. That the astronauts felt safe to use their watch in a life-or-death manoeuvre was a great testament to the reliability of the chronograph.
Because of the outstanding reliability required of every instrument in space flight, the first Omega Speedmasters with the calibre 321 were evaluated and approved by NASA in 1965. The calibre 321 was a Lemania 2310-based movement with a column-wheel and horizontal-clutch design. However, the watches that followed in subsequent years (such as the Speedmaster reference 145.022 that emerged in 1968) used the calibre 861 with cam-and-lever activation. The calibre 861 would also be incorporated into the next generation of Speedmaster Professionals — the tonneau-cased Mark II — which sadly never travelled into space. It is the same 861 movement that gives life to all Speedmasters since then, only now evolved into the calibre 1861 and its derivatives… except for the resurgent Speedy 321s, of course.
Of course, in an emergency when a chronograph watch plays a critical role — as the history of the Apollo 13 has shown — the calibre that powers the watch and the type of clutch it uses to activate the chronograph will likely not matter to the individuals involved. Although it’s generally accepted that a movement with a column-wheel activation system and a vertical clutch is more accurate and sophisticated than one with cams and levers, in practice, this distinction is merely academic. They are different technical approaches to a common goal. That’s the heart of all chronographs: the idea is that they work well, reliably, and repeatedly, no matter how they achieve it. In real life, one approach is just as practical as the other. And therein lies another charm of chronographs.
Such is the ubiquity and familiarity of chronographs that we take for granted and even underestimate them (not me, though). Unjustly so, I would add. Think about it: along with the delightful minute repeater, the chronograph is the only complication that works on-demand, that is when you want it to. Hence, it requires many energy and mechanical occurrences from the system that should not affect the watch’s basic functioning. This is why chronographs are a fascinating and important complication of remarkable complexity.
How a Chronograph Works
The chronograph is undoubtedly one of the most prevalent complications because it can be used almost any time. Most people do not realise that the chronograph mechanism is one of the most complex to design and manufacture, as there is no other type of watch complication that requires as much interaction from its owner.
All chronographs measure and display elapsed time. The chronograph mechanism, driven by the watch’s movement, controls a seconds hand that can be started and stopped to time an event. A secondary display records the elapsed minutes. Usually, two push-buttons on the case serve to operate and reset the chronograph to zero, although single push-button systems — where a single button controls the start, stop, and reset of the counter — are a technical and aesthetic delight.
So, what are the seals of quality when it comes to making a chronograph? Above all, watchmakers value the solidity of the watch, its reliability, accuracy and ease of use, particularly the smoothness of the chronograph pushers. The best way to understand why some chronographs feel different from others is to understand what happens when the chronograph is activated.
First, the brake which has been preventing the central seconds hand from moving is released. With that, the system cocks or re-adjusts the hammers, making the hands return to zero when the chronograph is reset; by doing this now, the watch is preparing for when the second pusher is pressed. That’s why you see so much movement in the calibre when you activate the start button — not only does the counter start to run, but the return-to-zero system is also armed. Moving these hammers is the main reason that starting a chronograph from rest can feel a bit hard; they have to be cocked, and that requires force. So that’s why stopping and starting the counter without setting it to zero seems easier.
At the same time that the system is being reset, the chronograph mechanism is engaged with the gear train, specifically the drive wheel which is in constant rotation. This occurs through a lateral/horizontal clutch or a vertical one. An oscillating pinion —invented by Edouard Heuer in 1887 — is an addition generally used in cam systems with horizontal clutches and is a practical and low-cost solution in chronograph making. A laterally coupled clutch engages the gears, whereas a stationary one — that of the chronograph — is linked to the drive wheel by means of an intermediate wheel to which it is always connected. When the chronograph is stopped, the transmission decouples from the chronograph mechanism using the clutch again, and the brake is applied. When the chronograph is reset, which can only be done after the chronograph is stopped (because there is a lock that prevents it from being activated), the brake is deactivated, and the hammers strike their respective cams and return all the hands to zero.
Integrated and Modular Chronographs
There are only two main types of chronograph movements: modular or integrated. The integrated chronograph is a movement designed to be a chronograph from the beginning. All chronograph functions are built-in, which is the most elegant solution that fits the fine watch archetype. Most watch lovers prefer it, but that does not disqualify its alternative, the chronograph module, which is practical and cost-efficient, making it possible for collectors to enjoy countless mechanical chronograph alternatives in all price ranges.
A modular chronograph uses a base calibre to which a chronograph module is added. This allows for more flexibility and allows for economies of scale in the base calibre production. Because of their architecture — and so as not to unnecessarily increase the entire movement’s thickness — the chronograph modules engage the counter via a horizontal clutch.
As we saw, the essential operating principle of chronographs is based on a connection between the chronograph wheel and drive wheel of the gear train, which is running at all times. While the first chronograph movements were composed of simple levers and rods, the two most frequent types of movements that still exist today are the column wheel and cam and levers.
The easiest way to explain cam and column-wheel systems is to see them as mechanical “switches” that turn the chronograph function on and off. The types of clutches — horizontal or lateral and vertical — are the ways in which the chronograph is engaged (more on that later).
In a column-wheel movement, a mechanism that looks like a small castle turret (or a chess rook) turns an increment with each click of the chronograph pusher. A mechanical finger falls between the teeth of the column wheel to activate the functions. The column-wheel mechanism — which, because of its three-dimensional shape, is more difficult to make than a simple two-dimensional lever — has a ratchet with large teeth interconnected via a hammer with its pusher.
When you press the start/stop button, the connecting lever turns the wheel one tooth at a time. On a higher level, three levers press against the pillars or columns. As the column wheel rotates in increments when the chronograph push-buttons are pressed, the levers fall in and out of the spaces between the pillars, activating the system’s different parts.
When the counter is started up, the column wheel contacts a coupling arm that basically connects the drive wheel to the chronograph wheel; simultaneously, the chronograph wheel is also released by the brake lever. While the system is in operation, the reset button is locked by the brake lever.
Then, when the stop button is pressed, the column wheel rotates in another position and causes the opposite effect to that described above: the brake lever moves and activates the brake on the chronograph wheel, while the drive wheel is disconnected from it by the dance of the hammers connected to the column wheel.
Pressing the reset push-button activates the reset hammers (armed from the first opposing one in operation), and the wheels and hands return to zero. Of course, in a flyback system (or retour en vol), a parallel system — also controlled by the column wheel — allows instant chronograph reset without the need for a stop, but that is the subject of another article.
A column wheel demands high precision in its making and also requires more parts (hammers and levers, pivots and springs) very delicately designed and sculpted to work. The result is a more precise operation and a better feel at the start/stop button. The user of a column-wheel chrono movement will no doubt notice its smooth and seemingly instantaneous response to button presses. Column-wheel chronographs have a reputation for being more expensive yet they are more desirable to watch collectors because of the level of quality and attention to detail in their manufacture. Nevertheless, watches such as the Omega Speedmaster Moonwatch — with no column wheel but with a cam-and-lever activation — or the oscillating pinion solution installed in the Valjoux 7750 chronographs have given column-wheel chronographs a serious run for their money. In fact, the cam-and-lever system has replaced many of the movements which utilised the intricate high-end column wheels to control the operation of chronographs.
A simpler and more economical solution, easier to produce, assemble and maintain, the cam system is very robust and does not require the demanding tolerances needed for a column wheel. Each time a chronograph button is pressed in this type of movement, it causes a heart-shaped cam (also known as the coulisse) to turn back and forth to start, stop or restart the chronograph. In this scheme, an intermediate wheel is always connected to the drive wheel of the base movement by means of a cam, which is always in one of two possible positions depending on the start/stop pusher’s operation. This cam is made of two parts, one upper, one lower, fixed together; the lower cam engages the start/stop functions; the upper one activates the reset function.
When the chronograph is activated, the control cam turns one position. It makes the system move the intermediate wheel — let’s remember that it is connected to the drive wheel — and puts it in contact with the chronograph wheel, starting it up at once. Due to the sudden connection and the usual difference between the sizes and masses of the teeth of the two wheels, the activation is abrupt. It can cause a very visible and disturbing jump of the chronograph seconds hand and a momentary loss of the oscillation amplitude of the balance wheel. Despite this, it is the most widely used system and has invited improvements, such as the aforementioned oscillating pinion integrated into the Valjoux 7750 calibre. With the oscillating pinion, the aggressiveness of the shock between the wheels is significantly reduced, minimising the jump of the chronograph seconds hand and the long-term wear of the system.
n general, the operation of a cam system is firmer, requires more effort to engage, and many users have claimed that it is not as pleasant to the touch (habit remedies everything, but whatever). Also, it is not recommended to use the function for long periods because of the constant wear between the coupling wheels and the higher energy expenditure. The vast majority of mechanical chronographs sold today use the Valjoux 7750, which was introduced in 1974, or variants of this movement.
So, between the column wheel and the cam-actuated system, which one makes a better watch? We say it is a matter of perspective. As mentioned, the column wheel is the finer device and the more traditional solution, while the cam-and-lever chronograph’s production and service costs are lower. But both systems work nicely, delivering pretty much the same usefulness.
Now let’s go further to explore the design of the chronograph coupling systems. In order for the chrono counter to be started, the chronograph wheel has to be connected to the gear train in one of two possible ways: via a horizontal or vertical clutch.
Chronographs based on the horizontal or lateral clutch work well in general and are visually very attractive and even enlightening for any curious mind. However, they suffer from the problem of sudden gearing of the intermediate wheel — the one connected to the drive wheel of the main train, which is always in rotation — with that of the chronograph, and the imperfect coupling of the wheels may result in a somewhat rough operation. That said, it is the most widely used design and the noblest watchmakers, such as Patek Philippe and Zenith, with their calibres CH 29-535 PS and El Primero respectively, have no qualms about using this proven architecture in their best chronographs.
It goes without saying that the horizontal clutch is also the most commonly used solution for thin calibres, as it allows the set of components to extend over a larger surface. However, there are very slim chronograph calibres — such as Piaget’s 880P and its derivations, like the 1160P — that dare to use a vertical clutch in their very thin movements, making this scheme even more noteworthy.
As its name indicates, with a vertical clutch, the chronograph mechanism’s coupling is positioned vertically, similar to the systems found in cars that connect the engine flywheel with the transmission. While horizontal clutches are visible, simpler and thinner mechanisms, the theoretical advantage of a vertical clutch is that there are no sharp teeth to engage or disengage — a mechanism that can lead to the notorious and ugly jump of the chronograph seconds hand, not to mention excessive wear and tear.
In a vertical-clutch system, the chronograph wheel and the drive wheel are located concentrically, sharing the same axis. The latter, in fact, is constantly running for as long as the watch is working. The vertical coupling clutch employs a pair of levers or arms that keep the chronograph wheel “floating” above the ever-rotating calibre drive wheel. When released, both arms allow the clutch to fall on the seconds wheel, which then starts to rotate, thanks to the friction between them. As an example, think of a vinyl record that is dropped onto a turntable. Inside the watch, when the clutch drops, both wheels begin to turn simultaneously. This offers significant advantages: precise starting and stopping of the seconds hand and the ability to use the chronograph function for long periods without affecting the watch’s accuracy due to minimal wear. Also, there is no loss in the balance wheel’s amplitude. Pressing the stop button causes the clutch arms to be inserted below the clutch to lift it, instantly disconnecting the chronograph wheel from the drive wheel and stopping the running of the chronograph seconds hand.
Are there disadvantages to vertical coupling? Firstly, they are usually found on slightly more expensive watches, although there are reasonably affordable options such as the Longines’ watches using the L688 or ETA A08.L01 movement. Secondly, the technical complexity of the vertical-clutch design cannot be visually appreciated by the typical watch wearer since the system — the wheels, the shared axis, the clutch arms — are usually hidden under the chronograph bridge, which in turn is obscured behind the oscillating mass in automatic watches. A horizontal-clutch design, in contrast, is mostly visible and allows the user to clearly see and understand the relationship between the components.
All things considered, though, the vertical-clutch and column-wheel system seems to strike the best balance between haute horlogerie savoir faire and practical use because of lessened wear on the components. But the horizontal clutch, particularly with cam-and-lever activation, offers significant advantages as well — most notably, in terms of costs. Ultimately, the choice of which chronograph to own is down to personal taste. What all chronograph lovers can agree on, however, is that the interactive nature of this complication makes the user an essential part of the magic of horology. Yes, the Internet watch forums are rife with debates on which is a more effective system, but every chronograph, no matter what system it uses, is a good watch if it does its job well. If the crew of the Apollo 13 were not quibbling about the mechanism that was inside Swigert’s Omega Speedmaster in a life-or-death situation, we should not be splitting hairs either…. Not too much, anyway.