Monochrome Watches
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Patek Philippe Ref. 5235 Annual Calendar Regulator

| By Frank Geelen | 5 min read |

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!

The Patek Philippe Ref. 5235 Annual Calendar Regulator features a dial with an unusual arrangement – large sweep minute hand combined with subsidiary hours at 12 o’clock and subsidiary seconds at 6 o’clock. Free-standing precision pendulum clocks with regulator arrangement kept the precise time in watchmaking workshops and observatories, for more than 200 years, until they were finally superseded by quartz- and radio-controlled reference instruments.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.

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Originally Patek Philippe wanted to use the legendary caliber 240 as base for their first regulator wrist watch, because it is a very thin self-winding movement. This 2.53 mm thick self-winding movement with mini-rotor features a its subsidiary seconds dial at 5 instead of 6 o’clock, which didn’t suit the ideas for the regulator arrangement. So Patek created the entirely new self-winding caliber 31-260 REG QA. The actual movement is 2.60 mm thick and the annual calendar is 2.48 mm thick, resulting in a total thickness of 5.08 mm. The basic movement is 0.07 mm thicker that the in 1977 developed caliber 240, but it is also the very first totally new basic movement designed to accommodate Silinvar components!

The new movement features four innovations. 

The oscillator in Silinvar

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. Silinvar components are totally anti-magnetic, remarkably shock-resistant, non-corroding, and require no lubrication. The Spiromax balance spring that is flat yet breathes absolutely concentrically thanks to its patented geometry with the Patek Philippe terminal curve. The Pulsomax escapement with Silinvar lever and escape wheel also feature enhance isochronism delivered by the Spiromax hairspring and the improved energy efficiency contributes significantly to higher rate accuracy and long-term dependability

A new going train – tooth by tooth

Patek Philippe’s engineers 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 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 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.

An unusual frequency of 3.2 hertz

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 means less friction between the fine wheel pivots and the bearing jewels, which enhances longevity and reliability.

An extra-long mainspring for power to spare

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.

In comparison with the 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%.

The new basic caliber incorporates an Annual Calendar mechanism that can be found on several other Patek Philippe models. The dial shows apertures for the day (between 10 and 11 o’clock), month (between 1 and 2 o’clock) and date (at 6 o’clock). A feature that I personally like a lot about annual calendars is that it recognizes 30-day and 31-day months and only needs to be corrected only once a year, on March 1.

Its case features the classic Calatrava silhouette that has defined 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 has a more contemporary size. The classic three-part case made of 18K white gold  features a bezel that is gently chamfered and the caseband is decorated with straight graining. The Ref. 5235 Annual Calendar Regulator comes on a night-blue hand-stitched alligator strap with square scales with 18K white-gold buckle with the Patek Philippe signature. The display back of the case allows the owner to admire the movement.

One last photo to enjoy the sheer beauty of this new Patek, the first with a regulator style arrangement and featuring an entirely new movement with the Silinvar components and a very unusual beat rate!

More information can be found on the Patek Philippe website.

3 responses

  1. I received my Regular last week. It is fabulous. It took almost three years since I first saw a picture and ordered this watch. Worth the wait

  2. Frank, Great article–I love my 5235 and you just made it that much better! One correction… Yes…you have to change the annual calendar on March 1st–only once per year… But let me add…only 3 out of 4 years! Bob

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