The Evolution of Patek Philippe's Calatrava Movement

The Evolution of Patek Philippe's Calatrava Movement

For more than 85 years, the Patek Philippe Calatrava has been widely regarded as the standard bearer for time-only dress watches. It dates back to the 1930s, a time of transformation wrought by the Great Depression. It was the watch that ushered in a new era for Patek Philippe with the two brothers Jean and Charles Stern at its helm. In contrast to the flamboyant styles of the previous decades as exemplified by the Gondolo, the Calatrava was round, yet unfaltering in its design, encapsulating the dynamics of modernism, namely Bauhaus – the ideas of “less is more” and “form follows function.”

While always keeping within the bracing paradigm of its elegant, minimalist philosophy, the Calatrava brimmed with many aesthetically differentiating details through the decades, from dial styles to case sizes. But equally, the movements as well as the order of priorities in designing them have evolved and shifted tremendously.

In charting the evolution of the most significant Calatrava movements, it’s apparent that their designs speak to intrinsically classic considerations in which form and function operate in a kind of recursive loop, right from the first 12-ligne hand-wound movement through to the brand’s first automatic calibre 12-600AT, the ultra-thin automatic calibre 240, culminating in the truly remarkable 30-255 in the newly launched Clous de Paris ref. 6119.

As a whole, this ensemble also serves as a broad survey of watchmaking – its preoccupations and progress through time from central seconds to automatic winding, slimness and ultimately high performance. Notably, for Patek Philippe, these pursuits were achieved while maintaining a high degree of care in construction and an exceptionally refined aesthetic that has shaped the conception of a dress watch movement as we know today.

The Hand-wound Movements of the Golden Age

The preeminent Calatrava ref. 96 was introduced in 1932. It was a small 31 mm watch that measured 9 mm in height. At that point in time, Patek Philippe relied on movements from LeCoultre in Le Sentier, so for the first two years of production, the Calatrava was equipped with a 12-ligne LeCoultre movement. As the company underwent a complete overhaul, the Sterns appointed Jean Pfister, a watchmaker and horologist, as the company’s technical director. Pfister was determined to build Patek Philippe’s in-house capabilities, and the calibre 12”’120 was the first movement developed under him. This movement powered all subsequent ref. 96 watches made between 1934 and 1973.

The Calatrava ref. 96
The Calatrava ref. 96
The in-house calibre 12-120 (Image: Bukowskis)
The in-house calibre 12-120 (Image: Bukowskis)

The calibre 12”’120 was characterised by a traditional Genevan architecture and was intended to uphold the reputation the firm had established with its pocket watches. As seen in most movements during that time, the calibre 12”’120 was designed with a subsidiary seconds, in which the fourth wheel, making one revolution a minute, is positioned at six o’clock to drive the seconds hand directly. This traditional layout optimises the volume of the movement by spreading out the moving parts on the same plane. The escape wheel and fourth wheel are held in place by their own bridge while a separate elongated bridge spanning the movement is designated for the second and third wheels.

The wheel train layout of the calibre 12-120
The wheel train layout of the calibre 12-120

Derived from pocket watches, this finger-bridge architecture was the prototypical design in hand-wound movements of the early 20th century. In contrast to full or three-quarter plate movements, a bridged design facilitates convenient servicing with its excellent visibility and access to individual components. At the same time, the configuration of the bridges and increased number of edges lends itself admirably to embellishment.

As a result, such multi-bridge constructions became the preserve of high-end watches or fell victim to cost-cutting measures after the Quartz crisis. Some notable details of the 12”’120 include the black-polished steel plate on the cock that holds the escape wheel as well as the shape of the bridges which allow for sensuous anglage and sharp inward angles.

A close-up of the main bridge with a sharp inner corner (Image: Phillips)
A close-up of the main bridge with a sharp inner corner (Image: Phillips)

It is equipped with a swan neck fine regulation system over a balance with screws for inertia adjustment. The balance cock features a wide circular hub (held in place by two screws to retain the cap jewel) that offers a large surface for black polish. This was a traditional design often found in pocket watches prior to the use of shock absorbers.

In 1949, Patek introduced the 12”’400 calibre, which was, for the most part, similar to the 12”’200 except for the design of its regulator and the additional shock-resistant suspension on the balance wheel.

The Patek Philippe calibre 12-400 (Image: Vintage Gold Watches London)
The Patek Philippe calibre 12-400 (Image: Vintage Gold Watches London)
The brand's first serially produced anti-magnetic watch, the ref. 3417, equipped with the calibre 12-400 (Image: Phillips)
The brand's first serially produced anti-magnetic watch, the ref. 3417, equipped with the calibre 12-400 (Image: Phillips)

The movement was later used in the brand’s first serially produced anti-magnetic watch, the ref. 3417, in 1958. It was later upgraded with a Gyromax balance wheel and antimagnetic materials such as beryllium and duo-chrome in 1960, earning it the designation 27-AM-400 (AM for anti-magnetic).

The Central Seconds

At the time, one of the brand’s most fascinating inquiries was its quest for central seconds. While having a centre seconds hand is customary in modern watches today, movements back then were designed with a subsidiary seconds in which the gear train terminated at six o’clock to drive a small seconds hand directly.

In 1939, Patek Philippe’s 12-ligne calibre spawned the 12-120 SC (SC designated seconde centrale), which was used in the ref. 96 as well as the 565 and the 570. The movement incorporated a sophisticated indirect centre seconds mechanism produced by Victorin Piguet. It was one of the earliest movements in watchmaking to feature a central second.

The Calatrava ref. 565 with an indirectly driven central seconds (Image: Phillips)
The Calatrava ref. 565 with an indirectly driven central seconds (Image: Phillips)
The calibre 12-120SC incorporating a notably elaborate indirect central seconds mechanism (Image: Antiquorum)
The calibre 12-120SC incorporating a notably elaborate indirect central seconds mechanism (Image: Antiquorum)

Visually akin to a chronograph, the mechanism comprised of three additional gears driven off the fourth wheel at six o’clock. The gears are located above the going train so as to relocate the seconds back to the middle. While this solution has become a standard practice to achieve an indirect central seconds, Victorin Piguet designed a notably elaborate set-up that included a pivoted lever to support an intermediate wheel.

As with all movements with an indirectly driven train including chronographs, there is a tendency for the seconds hand to flutter due to backlash in the motion of the wheels. To eliminate this, a tension spring visible on the right is used to apply a modest amount of pressure and maintain engagement between the wheels.

Later in 1949, Patek introduced the 27 SC, an ingenious movement with a directly driven central seconds. Although modern movements are usually designed with a central seconds in which the fourth wheel is positioned right in the middle to drive the seconds hand directly, this results in the centre (or second) wheel, which drives the minute hand, being positioned elsewhere. As such, an additional set of wheels – often driven off the third wheel – is once again needed to relocate the minutes back to the middle.

Logically, it is more efficient to design a movement with an indirectly driven minutes than an indirectly driven seconds as the fourth wheel is the fastest spinning wheel in the gear train and also the one with the least torque. Additionally, it is worth noting that the auxiliary wheels required in both approaches naturally contribute to the added height in the movement.

The calibre 27 SC in the Calatrava ref. 570 (Image: A Collected Man)
The calibre 27 SC in the Calatrava ref. 570 (Image: A Collected Man)

With the 27 SC, however, Patek Philippe avoided the drawbacks of both solutions by stacking the second and fourth wheels on the same axis in the middle, establishing both a directly driven seconds and minutes. As with either one of the aforementioned approaches, this is accomplished at the expense of the height as evidenced by the raised bridges from six to eight o’clock. However, it eliminates the need for additional gears as well as the associated consequences and necessary solutions. Additionally, this clever configuration also allows the movement to preserve the beautiful foundational architecture of the 12-120.

The calibre 27 SC achieves both a directly driven seconds and minutes by locating the wheel second and fourth wheels in the middle (Image: A Collected Man)
The calibre 27 SC achieves both a directly driven seconds and minutes by locating the wheel second and fourth wheels in the middle (Image: A Collected Man)

The Landmark Automatics

In 1953, Patek Philippe introduced its first self-winding movement, the calibre 12-600 AT (AT designated automatic winding) in the landmark ref. 2526. The watch was significant for combining three of the brand’s technical innovations – an automatic winding mechanism, a Gyromax balance and a water-resistant case.

The landmark ref. 2526 equipped with the brand's first self-winding movement, the 12-600 AT (Image: Phillips)
The landmark ref. 2526 equipped with the brand's first self-winding movement, the 12-600 AT (Image: Phillips)
The elaborately constructed calibre 12-600 AT
The elaborately constructed calibre 12-600 AT

The calibre 12-600 AT is widely regarded as one of the finest, most elaborately constructed automatic movements ever produced not only for its superior technical qualities but also its design and decoration. Notably, in contrast to Rolex’s first perpetual movement in 1931, the calibre 12-600 AT retained the traditional finger-bridge architecture found in Patek’s hand-wound movements – a design that eventually faded away with the rise of self-winding systems as the bridges and gear train had to be reconfigured to accommodate the rotor and equally, the advent of sports watches which logically entailed – although not a universal truth – larger bridges for greater stability. Furthermore, it boasts a solid 18k gold rotor featuring a beautiful engine-turned motif.

To further differentiate itself from the other automatic systems in the market, Patek Philippe devised a complex, more efficient winding mechanism. It was centred on an eccentric wheel that is driven by the rotor. This wheel drives a pair of rockers that carry a pair of pawls, which in turn interact with the teeth of a ratchet wheel, winding the mainspring.

Oddly, a swan neck regulator was used in parallel with a Gyromax balance. This could be because the proprietary free-sprung balance was still in its nascent phase, so Patek Philippe opted for a dual solution until it was confident enough to use the balance as a standalone technology.

Introduced in 1951, the Gyromax is characterised by turnable weights with a cutout design to ensure that the one end is heavier. Inertia can then be increased by pointing the heavier side outwards. Impressively, the balance is also fitted with an overcoil hairspring. These were significant refinements in those days and were rarely found in the same movement.

Further improvements were made with regards to the complex winding system and it was later was succeeded by the legendary 27-460. This version saw some other refinements including a ball bearing instead of the jewelled rotor bearing as well as an adjustable stud holder. It was also in this movement that the Gyromax came into its own and was used independently.

The Ultra-thin Hand-wound

The enthusiasm for marrying function and style paved the way for the rise of ultra-thin watchmaking in the 1950s and 1960s. Patek Philippe’s response was the Calatrava ref. 3520 in 1965. It was characterised by a Clous de Paris, or hobnail bezel and advertised as “the flattest waterproof watch in the world” at the time of its introduction.

The ultra-thin Calatrava ref. 3520 with the characteristic hobnail bezel (Image: Watch Box)
The ultra-thin Calatrava ref. 3520 with the characteristic hobnail bezel (Image: Watch Box)

Over the course of its 25 year production, it was powered by the calibre 175 and subsequently the 177 in 1977. Both movements were derived from the ultra-thin and compact Frederic Piguet calibre 21 which was the prototypical ultra-thin manual movement that dates from the dawn of wristwatches and was adapted by a wide variety of brands ranging from Cartier to Rolex.

The Patek Philippe calibre 177 based on the venerable F. Piguet 21
The Patek Philippe calibre 177 based on the venerable F. Piguet 21

It measured 9-ligne in diameter and was either 1.75mm or 1.77mm high. The calibre is notable for both its conventionally solid and aesthetically pleasing construction despite being under 2 mm.

It is distinguished by its Lépine construction whereby the fourth wheel is positioned at nine o’ clock in line with the winding stem, with the balance in turn mounted on the right.

Thus, due to the atypical position of the fourth wheel, the subsidiary seconds hand was often omitted in the watches it inhabited, and central seconds was avoided to preserve the original intent of the calibre, which was slimness.

The movements offered a power reserve of approximately 42 hours and was fitted with a Gyromax balance that ran at 2.5 Hz in the cal. 175, while the cal. 177 beats at a more modern 3 Hz.

The Workhorse Hand-wind

In 1974, Patek Philippe introduced the calibre 215 PS, a 10-ligne movement that was conceived as a successor to the 12-120 and the suite of other 10-ligne movements such as the cal. 23-300. It remains a staple in the Calatrava line and can be found in many notable references such as the ref. 3960, ref. 3919, ref. 5196, ref. 5116 and ref. 5119.

The ref. 3960 with an Officer's case, launched to commemorate the firm's 150th anniversary in 1989 (Image: Christie's)
The ref. 3960 with an Officer's case, launched to commemorate the firm's 150th anniversary in 1989 (Image: Christie's)
The calibre 215 PS powers a majority of modern Calatrava models
The calibre 215 PS powers a majority of modern Calatrava models

With the calibre 215, there was a distinct focus in improving chronometric performance. At the time of its launch, it was the first calibre to have a Gyromax balance that ran at a frequency of 4 Hz, up from the usual 3 Hz or less before, which improved the stability of the balance motion in the face of shocks, while offering a respectable power reserve of 44 hours.

Though the layout of the geartrain is virtually the same as in the 12-120, the shape as well as configuration of the bridges are no longer as complex. The full bridge, which carries the upper pivots for the second and third wheels, have a less pronounced shape which eliminates the sharp inner corner while the fourth and escape wheels now share a common bridge as opposed to having individual finger bridges.

However, it successfully manages a tricky balancing act between performance and aesthetics with respect to cost.  Without a doubt, this is a reflection of the seismic changes brought about by the Quartz crisis, which had changed the rules of the game in terms of movement design, with performance now playing a more critical role.

The Workhorse Automatic

In 2006, Patek introduced the ref. 5296, a Calatrava that was closely inspired by the ref. 96 but was conceived to meet modern demands. It was powered by the workhorse automatic calibre 324 SC, which came with an indirect central seconds as well as a date display. The movement is a successor to the calibre 315 and powered a majority of the Nautilus from 2007 to 2019.

The ref. 5296R with a 38mm case, a central seconds and a date display
The ref. 5296R with a 38mm case, a central seconds and a date display
Patek Philippe calibre 324 SC
Patek Philippe calibre 324 SC

As compared to Patek’s earlier automatics, this lineage of calibres adopts a more functional design with larger bridges and is often found in more robust watches. Measuring 27mm wide, the calibre 324 is armed with all of the brand’s modern technical innovations including a Gyromax balance, which operates at a frequency of 4Hz and is attached to a Spiromax hairspring.

The Patek Philippe Calatrava - 324 SC employs an ingenious solution to include an indirect central seconds without any additional gears.
The Patek Philippe Calatrava - 324 SC employs an ingenious solution to include an indirect central seconds without any additional gears.

Like the calibre 315, it features an indirect central seconds. However, this solution of achieving a central seconds is particularly noteworthy as it does not entail an axuiliary geartrain. Instead, the third wheel drives a pinion in the middle for the central seconds. Even more unusual is the fact that great (second) wheel is not located in the middle. Rather, it is positioned at 10 o’clock from the rotor hub when viewed from the caseback. This frees up space in the middle to accommodate the winding mechanism, allowing the movement to maintain a slim profile of just 3.3mm high. Meanwhile, the third wheel drives the minute wheel on the dial side.

The Ultra-thin Automatic

The ultra-thin self-winding calibre 240
The ultra-thin self-winding calibre 240

Introduced in 1977, the beautifully engineered self-winding calibre 240 can be found in all its splendour in one of the most distinctive modern Calatrava models – the 6000/ 6006G. Though the movement has been used in other Calatrava watches such as the ref. 5120, it is this model in which the distinctive modernity of the movement is embraced in the design of the dial, demonstrating coherence and unity.

The ref. 6006G, one of the most distinct modern Calatravas.
The ref. 6006G, one of the most distinct modern Calatravas.

The calibre 240 was conceived in the thick of the Quartz Crisis with the intention of demonstrating an elegance in engineering that would eclipse the precision of quartz. It measures a mere 2.53 mm thick, making it even slimmer than the hand-wound 215 PS. To maintain its height, the rotor had to be made from solid 22k gold to ensure sufficient inertia. The rotor winds the barrel unidirectionally to eliminate the need for reverser gears, thus reducing friction.

What distinguished the ultra-thin calibre 240 from other micro-rotor calibres at that time was its supremely elegant architecture wherein the entire transmission system, from the automatic winding wheels and barrel to the going train and the balance wheel, were arranged in a shape of a crescent on one side of the movement, leaving room for the off-centred micro-rotor on the same plane.

Notably, instead of positioning the centre wheel in the middle to drive the minute hand directly, the centre wheel in the 240 is located off-centred on the left to make way for a larger rotor and minimise overlapping, thereby reducing its height. The second wheel pinion drives the minute wheel on the dial side which in turn drives the cannon pinion. This is a deviation from a standard movement where the centre wheel drives the cannon pinion directly.

As a result of this crescent-shaped gear train arrangement, the fourth wheel, onto which the seconds hand is mounted, is located in a rather unusual position at eight o’clock when viewed from the case back. Hence, with the exception of a few watches, most notably the 6000 and 6006, the seconds hand would typically be omitted.

While the self-winding Calibre 240 has been optimised in many respects since its debut, it still retains its original structure. It runs at a frequency of 3Hz, but now with a Spiromax hairspring for improved isochronism. The tooth profiles of the going train were also further optimised to reduce wear, contributing to its 48-hour power reserve as well as boosting long-term reliability.

The High Performance Hand-wound

The Clous de Paris ref. 6119 with a 39 mm case equipped with the superb calibre 30-255 PS
The Clous de Paris ref. 6119 with a 39 mm case equipped with the superb calibre 30-255 PS

Finally, Patek Philippe’s expertise in the various areas of movement design culminated in the brilliantly constructed calibre 30-255 PS in the new “Clous de Paris” ref. 6119. The movement is the perfect blend of art and science, a triumph both technically and optically.

The brilliantly engineered calibre 30-255 PS with double barrels and a balance with impressively high inertia.
The brilliantly engineered calibre 30-255 PS with double barrels and a balance with impressively high inertia.

It measures 2.55mm in height, making it as slim as the 215 PS, but at 13.7 lignes, it is significantly larger in width, allowing it to accommodate double barrels that unwind in parallel. In contrast to barrels that are connected in series to achieve a longer power reserve, the objective of parallel barrels is to offer greater and more consistent torque. Additionally, with half the power stored in each barrel, they can be made flatter than a typical barrel.

In this case, a greater torque was required to power a balance wheel with a frequency and inertia that are comparatively higher than other movements from Patek Philippe. It beats at a rate of 28,000 vibrations per hour and a moment of inertia of 10 mg/cm2 – twice the inertia of the brand’s other 4 Hz movements. The combination of a high balance power and a power reserve of 65 hours is all the more impressive in light of its height and is a testament to its exceptional design.

To maintain the height of the movement, a tiny central pinion was used to drive the minute hand. This helps in minimising stacking and in optimising the horizontal space available in the movement by spreading out the wheels on the same plane. The central pinion, in turn, drives the actual centre wheel via an intermediate wheel.

Apart from maintaining the height of the movement, the two pinions, which are small and solid, are also ideal in the face of high torque, as they effectively serve as the great wheel of the movement right after the barrels. The spokes of the wheels eventually vary down the gear train, with the third and fourth wheels being the thinnest and lightest. Impressively, the movement also incorporates a stops-seconds mechanism that is made up of two pivoted levers along the periphery of the gear train for precise time-setting.

Additionally, because of the multiplicity and sinuosity of the bridges and cocks, the movement is visually impressive and ultimately represents a masterclass in delivering high performance with a truly inspiring design.

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