Patek Philippe’s new Ref. 5235 Annual Calendar Regulator embodies a number of novel facets never before featured in the manufacture’s collection. It is the first Patek Philippe wristwatch with a regulator dial, characterized by a sweep minute hand, a subsidiary hour dial at 12 o’clock and a seconds subdial at 6 o’clock. The heart of the watch is the new caliber 31-260 REG QA, the first ultra-thin self-winding Patek Philippe movement with a mini-rotor that displays the subsidiary seconds at 6 o’clock. It is also the very first totally new basic movement designed to accommodate Silinvar® components: The escape wheel and the lever of the Pulsomax® escapement as well as the Spiromax® balance spring are made of the innovative silicon-based material. The new wristwatch is endowed with an Annual Calendar that displays the month, day, and date in apertures and ranks among Patek Philippe’s most popular complications.

The Patek Philippe Ref. 5235 Annual Calendar Regulator clearly affirms the manufacture’s philosophy according to which the paramount purpose of a watch is to keep the time as accurately and reliably as possible. The dial with the unusual arrangement – large sweep minute hand combined with subsidiary hours at 12 o’clock and subsidiary seconds at 6 o’clock – pays tribute to the prominent free-standing precision pendulum clocks that for more than 200 years kept the precise time in watchmaking workshops and observatories until they were finally superseded by quartz- and radio-controlled reference instruments. When adjusting their timepieces, watchmakers needed an unobstructed view of the seconds hand, which is why the hour display was moved to an off-center location where it would not sweep over and thus partially cover the seconds dial for several hours in the course of a day. One of the finest examples of this type of freestanding precision clocks is the Patek Philippe & Co. regulator built at the beginning of the last century. For many years it has been keeping the time unperturbed – second by second – in the office of Philippe Stern, the company’s honorary president.

To configure the face of a regulator clock with three separate displays for the hours, minutes, and seconds in a wristwatch format was a totally new venture in the Patek Philippe cosmos, not just from a design point of view. The plan was to set the stage for further innovations based on this novel layout. The legendary caliber 240 would have been the ideal choice for the assignment which called for a very thin self-winding movement, but most unconventionally, its subsidiary seconds dial is positioned at 5 instead of 6 o’clock. Launched in 1977 and featuring a 22K gold mini-rotor recessed in the main plate, the 240 movement is only 2.53 mm high; it still ranks among the thinnest self-winding calibers on the market and thus provided valuable inspiration for the new development. With the assets of its dependable predecessor and several trailblazing innovations, Patek Philippe’s new self-winding caliber 31-260 REG QA has everything it takes to define a new benchmark. Squarely centered between the middle of the movement and its outermost circumference, the size of the seconds subdial at 6 o’clock was maximized for optimum legibility – another homage to Patek Philippe’s philosophy as regards the equilibrium of timekeeping indications.

For the first time in the history of Patek Philippe, a movement was designed from the very beginning to accommodate oscillator components crafted from Silinvar®, a high-tech material derived from silicon. One of them is the Spiromax® balance spring that is flat yet breathes absolutely concentrically thanks to its exclusive and patented geometry with the Patek Philippe terminal curve. It controls the division of time by the Pulsomax® escapement whose Silinvar® lever and escape wheel also feature totally new geometries developed by Patek Philippe and for which patent applications have been filed. The enhanced isochronism delivered by the Spiromax® hairspring and the improved energy efficiency provided by the Pulsomax® escapement contribute significantly to higher rate accuracy and long-term dependability. Additionally, Silinvar® components are totally anti-magnetic, remarkably shock-resistant, non-corroding, and require no lubrication.

But Patek Philippe’s engineers wanted more than a new oscillator. They totally revamped the going train, the wheels and pinions between the mainspring barrel and the escape wheel. The shapes of the wheel teeth and the leaves of the pinions were analyzed in-depth, recalculated, and individually redesigned for the center wheel, the third wheel, and the fourth wheel with their respective pinions. These new profiles improve the meshing of wheel teeth and pinion leaves, reduce friction, increase the tolerance range for varying axis distances, and boost the efficiency of energy transmission from the spring barrel to the escape wheel. The result is a perceptible improvement of energy conversion efficiency with a concurrent reduction of wear.

The innovative efficiency-boosting and isochronism-improving technologies of the new regulator caliber 31-260 REG QA entail further positive consequences. While the classic self-winding caliber 240 beats at a rate of 21,600 semi-oscillations per hour, the frequency of the new movement was increased by nearly 10% to 23,040 vph, equivalent to 3.2 Hz, and at the same time, its power reserve was increased. In turn, a higher frequency makes it possible to more easily adjust the rate accuracy to - 3/+2 seconds per 24 hours as stipulated by the Patek Philippe Seal. Concurrently, thanks to the greater energy efficiency of the going train and escapement, it was possible to reduce the tension of the mainspring and thus the shear forces to which the wheels are exposed. This diminishes friction between the fine wheel pivots and the bearing jewels, further enhancing longevity and reliability. These two aspects are crucial for compliance with the Patek Philippe Seal and essential prerequisites for a watch that will be cherished by family members across generations.

Thanks to the energy efficiency of the caliber, it proved possible to choose a softer but also longer mainspring. So despite its increased frequency and the deployment of only one mainspring barrel, the new caliber 31-260 REG QA has a power reserve of up to 60 hours as opposed to a maximum of 48 hours for the caliber 240. The extended length of the mainspring has another advantage: its torque curve stays much flatter as it relaxes, so the amplitude of the balance and thus its rate remain stable most of the time between the fully wound and the fully unwound states. The result: greater rate accuracy for a longer period of time. And the option to set the watch aside for an entire weekend without having to readjust the time and the calendar on Monday morning.

Patek Philippe introduced further innovations to maximize the life and long-term reliability of the new Annual Calendar Regulator. Like all self-winding Patek Philippe movements, the caliber 31-260 REG QA can also be manually wound. However, the manual winding mechanism is always automatically uncoupled as long as the self-winding mode is active. This increases its winding power and reduces wear. In addition, the crown wheel of the manual winding mechanism was upgraded with a new toothing mechanism that reduces wear, improves efficiency, and optimizes the suppleness of the winding process. Moreover, the 22K gold mini-rotor recessed in the plate is 0.3 mm thicker than the one in the caliber 240 movement, which increases its mass and winding power. Decorated with Geneva circular graining, it is also a miniature masterpiece from the aesthetic point of view.

In comparison with the meanwhile 34-year-old caliber 240, the new caliber 31-260 REG QA beats at a 10% higher frequency and has 25% higher power reserve, which adds up to an efficiency increase of about 30%. This performance emphasizes the ample potential of mechanical watches and in times of global energy debates serves as a role model because it proves that even in traditional disciplines such as classical mechanics, substantial efficiency gains are still realistic.

The new Ref. 5235 Annual Calendar Regulator measures time with an accuracy of seconds, but it also correctly displays larger intervals of time. The new basic caliber incorporates an Annual Calendar mechanism that has been one of the manufacture’s bestsellers since it had its debut 15 years ago. This useful complication that displays the day, month, and date in three large apertures automatically recognizes 30-day and 31-day months and only needs to be corrected once a year: on March 1. On account of this calendar cadrature, the caliber designation is 31-260 REG QA; the movement consists of 320 parts (basic caliber 181, Annual Calendar 139), measures 5.08 mm in height (basic caliber 2.60 mm, Annual Calendar 2.48 mm), and has a diameter of 33 mm (basic caliber 31.74 mm, Annual Calendar 33.00 mm). The dimensions are ideal for a wristwatch conceived to be timelessly elegant.

Despite the unusual regulator layout of the dial, the new Patek Philippe wristwatch is as fetchingly graceful as all the timepieces crafted in the workshops in Geneva. Its case features the classic Calatrava silhouette that has defined the quintessential round wristwatch for nearly 70 years. Thanks to the ultra-thin movement, its height is a mere 11 mm, astonishing for a self-winding watch with an Annual Calendar. With a diameter of 40.5 mm, it is endearingly poised and tastefully contemporary. The classic three-part case ensemble with the bezel, the band, and the back in 18K white gold is a prime example of the Bauhaus philosophy expressed by the adage "form follows function." The bezel is gently chamfered and the caseband is decorated with straight graining – a perfect match with the satin-finished dial. The slightly sloped lugs extend the bezel’s chamfer, optimizing the contour of the watch for a snug fit on the wrist. It is worn on a precious hand-stitched night-blue alligator strap with square scales. The classic 18K white-gold prong buckle that secures the strap is engraved with the Patek Philippe signature. The display back of the case allows the owner to admire the movement with its exclusive components and lavish decorations: the new oscillator assembly with the Pulsomax® escapement and the Spiromax® balance spring as well as the mini-rotor decorated with Geneva circular graining, the Geneva striping on the beveled bridges, and the gold-filled engravings.

The sapphire-crystal glass protects the inimitable face of the new Patek Philippe Ref. 5235 with its characteristic sweep minute hand, the subsidiary hours dial at 12 o’clock, and the amply dimensioned subsidiary seconds dial at 6 o’clock. The large aperture displays of the Annual Calendar are arranged on a circle that is concentric with the bezel: the day of the week at 10 o’clock, the month at 2 o’clock, and the date at 6 o’clock. Engraved in the dial, the PATEK PHILIPPE GENEVE signature is aligned with the horizontal axis at 3 o’clock. Depending on the angle of the incident light, it changes in contrast from deep black to a silvery gray that seems to be just a gentle shadow on the textured dial. Blue transfer-printed numerals, markers, and scales always assure excellent legibility of the time. The railway track minute scale as well as the subsidiary dials for the hours and seconds have a brighter silvery gray background that stands out against the darker silvery gray central portion of the dial with the short blue 5-minute markers. Crisp Arabic numerals, blued-steel baton-style hands and blue calendar indications on white backgrounds underscore the cool technical elegance of this 2011 wristwatch that salutes the ultra-precise freestanding regulator clocks of old. The two-tone silvery gray dial features a vertical satin finish, and the two subsidiary dials scintillate with circular graining.

The new Patek Philippe Ref. 5235 Annual Calendar Regulator is yet another manifestation of how consummately the Geneva workshops master the amalgamation of avant-garde aesthetics with timeless elegance. The innovative personality of this watch is based on much more than appearances: it is derived from a mechanical heart that sets new standards in horology. Absolutely Patek Philippe-like.