Patek Philippe Aquanaut 5167 (5167A-001)

With its new Ref. 5950A split-seconds monopusher chronograph, Patek Philippe yet again presents a concept never before realized in this way: the combination of an individually crafted ultra-thin rattrapante chronograph with a case in stainless steel - a tribute to chrome steel as a case material in its own right.
In haute horlogerie, stainless steel today is just as highly regarded as are platinum and the various hues of gold. This is affirmed by diamond-studded ladies' watches, by the success of the legendary Nautilus, and by the impressive auction house records established by historic Patek Philippe steel watches from the 1940s. The profound respect with which Patek Philippe watchmakers handle stainless steel is easy to see when looking at a chronograph movement of the Genevan manufacture through a magnifying glass. Every single steel part of the elaborate calibers is finished with the utmost in craftsmanship. So it stands to reason that a movement with such meticulous finissage lavished on its steel components can legitimately be cased in steel. With the Ref. 5950A (A stands for acier, the French word for steel), Patek Philippe has made a smart decision, as it did long ago with the Nautilus and the Twenty~4®.
Caliber CHR 27-525 PS: the world's thinnest rattrapante movement.
One of the salient features of the new Patek Philippe split-seconds monopusher chronograph is the case, which is thinner than that of many ordinary three-hand watches. This is due to the exquisite CHR 27-525 PS movement with which the manufacture set a new global record in 2005 for the thinnest column-wheel chronograph caliber ever made. As usual at Patek Philippe, the caliber designation tells a story: CHronograph Rattrapante, 27 mm diameter, 5.25 mm height, seconds subdial (PS stands for petite seconde). A separate department was set up in 2003 explicitly to develop this very first proprietary chronograph movement. However, its objective was not to break a world record; it was to explore innovative solutions for Patek Philippe's future chronograph calibers. One of the new facets was the continuously running 60-minute counter which is driven directly by the cannon pinion. When the chronograph is operating, the minute-counter wheel is powered by the setting wheel that is concentrically and freely mounted on the minute-counter arbor. Power transmission relies on two friction springs between the minute-counter wheel and the arbor of the setting wheel. The force exerted by the friction springs on the chronograph-wheel arbor to suppress chronograph hand vibrations is compensated by the elimination of friction between the minute-counter wheel and the setting wheel arbor. When the chronograph is switched off, the minute-counter wheel is halted by the brake or the return-to-zero hammer, and the arbor of the setting wheel can idle freely between the two friction springs. Thus, the movement design kills two birds with one stone and not only saves height but also provides automatic equalization of the torque differences between the running and stopped states of the chronograph.
Time-tested toothing
The ultra-thin rattrapante movement has another exclusive asset: the patented toothing geometries for the chronograph wheels (driving, clutch, and seconds wheels). Thanks to the patented toothing, the teeth execute a rolling motion while engaged instead of scraping against each other. This reduces wear and optimizes the overall functionality of the chronograph:
- Minimized backlash suppresses chronograph hand vibration and reduces the loss of torque caused by the friction spring in the base movement.
- No hand quiver or rebound caused by the engagement of the clutch wheel with the chronograph wheel when the chronograph is started.
- Minimized risk of tip-to-tip contacts of the teeth.
- No tip-to-flank contact, improved efficiency, reduced friction.
All of these advantages improve the longevity and the long-term reliability of the watch while preserving its value.

rtisanally crafted, one by one.
Every single CHR 27-525 PS movement is manually crafted in the manufacture's haute horlogerie ateliers. Each one is composed of components that are individually filed, chamfered, polished, adjusted, and finished. When all the parts are ready, they are assembled in a so-called repassage en blanc procedure, after which all functions are tested. Subsequently, the entire movement is disassembled again. Once all parts have been meticulously cleaned, they are reassembled, lubricated, and fine-tuned. Thus, using ancestral production methods, Patek Philippe's watchmakers create horological masterpieces that exceed the expectations of even the most discerning connoisseurs.
Noble steel.
Ordinarily, horological bijoux like this ultra-thin split-seconds monopusher chronograph movement are integrated in precious-metal cases. But Patek Philippe is always good for a surprise, as in 1976 when the manufacture launched its casually elegant Nautilus model with a provocative headline: "One of the world's most expensive watches is made of steel." The Twenty~4® followed in the 1990s with a novel combination of steel and diamonds. And now, the Ref. 5950A rattrapante chronograph is here, with a cushion-shaped case in solid stainless steel that is water-resistant to 30 meters. The sapphire-crystal glass is cushion-shaped as well and slightly cambered, as is the display back. It affords a view of the breathtaking mechanisms that constitute the world's thinnest split-seconds chronograph with columnwheel control. The caliber is framed by a satin-finished surround with gold-filled engravings. Owners who are overwhelmed by so much beauty can have the sapphire-crystal case back replaced with the solid metal back that is supplied with the watch. The steel bbox is worn on a hand-stitched brown alligator strap with rectangular scales. Its prong buckle in 18K white gold is decorated with a black-lacquered engraving.

A functionally elegant dial.
The matt silvery sheen of the dial of the Ref. 5950A matches the deep gloss of the polished steel case. The crisp railway track minute scale emphasizes the masculine, technical look of the split-seconds chronograph. The four dial corners between the circular minute scale and the cushion-shaped bezel are decorated with with fine black-lacquered engravings that add a touch of graceful elegance.
time and lap-time measurements are performed with black oxidized, counterbalanced chronograph and rattrapante hands.
The time of day is indicated with two elegant, blackened leaf-shaped hands in 18K white gold that point at applied Breguet numerals, also in blackened 18K white gold. The watch has two subdials with intricate circular guilloche patterns: the running seconds are displayed at 9 o'clock, and the continuously running 60-minute counter is positioned at 3 o'clock. Both leaf-shaped subdial hands are made of black oxidized 18K white gold to match the overall personality of the watch. Patek Philippe's Ref. 5950A split-seconds monopusher chronograph is a further manifestation of the manufacture's independence. It has taken the liberty to present a stopwatch that in a fascinating way violates the conventions of haute horlogerie and creates its own market segment. The Ref. 5950A features a stunningly thin rattrapante movement produced one at a time by the most gifted watchmakers and cased up in stainless steel. But both the caliber and the case are finished to such a degree of perfection that they are symbiotic - as befits a creation signed by Patek Philippe.