This past March, at Baselworld 2012, Patek Philippe showed off their first ever regulator timepiece, the Ref. 5235 Annual Calendar Regulator. Consisting of a central minute hand, a subsidiary seconds dial (at 6 o’clock) and a subsidiary hour hand at 12 o’clock – the regulator dial separates the different time functions.

Regulator timepieces were used historically, to keep time as accurately as possible, specifically at workshops and observatories – where accurate timekeeping was paramount. Furthermore, to animate this all new functionality, Patek Philippe watchmakers created an all-new manufacture movement.

“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.”

The Ref. 5325 features an  annual calendar function, which automatically recognizes 30-day and 31-day months and only needs to corrected once per year. To make the adjustment, corrector buttons are located on the upper left quadrant of the case flank: Date between 9 and 10 o’clock, Month at 10 o’clock, Day at 9 o’clock (comes with correction stylus in ebony and 18K white gold).

Powering Ref. 5325 is Caliber 31-260 REG QA, an ultra-thin self-winding movement with an Annual calendar with aperture displays for the month, day of the week, and date. The in-house caliber consists of 320 parts (basic caliber 181, Annual calendar 139), 29 jewels, a power reserve of 60-hours and an unusual frequency of 3.2 Hz (or 23,040 VPH). This is the first time in Patek’s history that a movement was designed from the very beginning to accommodate oscillator components crafted from Silinvar®, a high-tech material derived from silicon.

The Spiromax® balance spring and Pulsomax® escapement both utilize Patek’s proprietary Silinvar® material. “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.”

Additional innovations include an extra-long mainspring, which allows for a 60-hour power reserve, with just one mainspring barrel. A new going train was designed in order to increase efficiency and to reduce wear. A 22K gold micro-rotor unidirectionally winds the mainspring.

Thanks to the ultra-thin movement, Ref. 5325 is presented in a very thin case. The 5325 has a fully polished 18K white gold case that measures 40.5 mm in diameter, and thanks to an ultra-thin movement, a height of only 11 mm. “The bezel is gently chamfered and the caseband is decorated with straight graining – a perfect match with the satin-finished dial.” The two-tone silvery gray dial features a vertical satin finish, and the two subsidiary dials have circular graining.

Hand-stitched night-blue alligator strap with 18K white gold prong buckle, engraved with Patek Philippe. Water-resistance 30 meters.

Retail is $53,600.

Posted by:Jason Pitsch

Jason is the founder of Professional Watches and specializes in writing, product photography, and digital marketing.