Audemars Piguet Openworked Perpetual Calendars

Audemars Piguet has formally announced the retirement of the historic Calibre 5135, signaling a significant shift in its approach to high-complication manufacturing with the introduction of Calibre 7139. This new in-house, selfwinding, openworked perpetual calendar movement represents a consolidation of mechanical innovations developed over the last decade, specifically leveraging the ultra-thin architecture pioneered in the RD#2 concept. The movement debuts in two distinct 41mm chassis: a Code 11.59 by Audemars Piguet reference executed in 18-carat white gold and black ceramic, and a Royal Oak Selfwinding Perpetual Calendar model that integrates titanium with Bulk Metallic Glass (BMG). These releases mark a pivot toward prioritizing ergonomic utility in grand complications, moving away from the fragile adjustment mechanisms that have historically characterized the perpetual calendar genre.

The introduction of Calibre 7139 is not merely an aesthetic update but a fundamental re-engineering of the perpetual calendar’s user interface. Historically, perpetual calendars have relied on a series of recessed correctors located on the case flanks, requiring a stylus or tool to adjust the day, date, month, and moon phase. This traditional configuration, while mechanically standard, posed risks of scratching the case or damaging the movement if engaged during the gear train's changeover cycle. The Calibre 7139 eliminates these external correctors entirely, integrating all adjustment functions into the crown. This "all-in-one" correction system allows the wearer to cycle through winding, time-setting, and calendar adjustments via four distinct crown positions, a feature that significantly alters the water-resistance architecture and case complexity of the watch.

The Case and Dial

The Code 11.59 reference (26443NB.OO.D002CR.01) presents a complex case study in material contrast and assembly. The 41mm architecture utilizes an 18-carat white gold bezel and caseback, which sandwich an octagonal case middle crafted from black ceramic. The ceramic component is not merely a decorative insert but a structural element that defines the watch's profile. Ceramic, known for its Vickers hardness rating significantly higher than that of gold or steel, provides scratch resistance in the area most prone to impact, while the gold bezel allows for the high-polish finishing that frames the dial. The lugs are skeletonized and welded to the bezel, bypassing the case middle entirely, a construction method that requires precise tolerance management to ensure structural rigidity and water resistance, which is rated at 30 meters for this model.

In contrast, the Royal Oak reference (26685XT.OO.1320XT.01) employs a more industrial materials science approach, pairing a titanium case and bracelet links with Bulk Metallic Glass (BMG) for the bezel, caseback, and bracelet studs. BMGs are amorphous metal alloys that are cooled rapidly during manufacturing to prevent crystallization. This lack of crystal structure imparts the material with high strength, elasticity, and superior resistance to corrosion and wear compared to standard stainless steel. Visually, the BMG components accept a mirror polish that reflects light with a distinct intensity, creating a sharp visual demarcation against the satin-brushed surfaces of the titanium case. The decision to use BMG for the bezel is functional; as the leading edge of the watch, the bezel absorbs the majority of deflection impacts, making the hardness of the palladium-based glass alloy a practical asset for long-term preservation of the finish.

The dial layout for both models has been reconfigured to accommodate the architecture of the Calibre 7139, departing from the layout of previous generations. The calendar indications have been shifted to a "European" arrangement: the date is positioned at 12 o’clock, the day at 9 o’clock, and the month at 3 o’clock. This is a crucial ergonomic update, as the date—the most frequently read indication—is now central and driven by a wheel with 31 custom-made teeth of varying sizes to manage the "progressive step" mechanism. At the 9 o’clock subdial, a day indicator now houses a simplified 24-hour display, aiding in the setting process. Crucially, a red sector located between 21:00 and 03:00 warns the user against manual adjustment during the date-change mechanism's engagement window, although the movement is designed to disengage effectively to prevent damage.

Visual inspection of the dials reveals the extent of the openworking. The Code 11.59 features transparent grey subdials with smoked external zones, providing legibility without obscuring the rhodium-toned gear train beneath. The moon phase at 6 o'clock utilizes a laser-ablated image on an aventurine disc, simulating a star field, which offers a textural contrast to the industrial finishing of the bridges. The Royal Oak model utilizes a similar sapphire dial concept but introduces pink gold accents on the hands, hour markers, and bridge bevels, providing a warmer tonality against the grey titanium and BMG. The week indication, printed on the inner flange, has also been recalibrated to begin with "1" at the 12 o'clock position, correcting the misalignment found in previous iterations where the "52" was prominent at the top of the dial.

The Movement

The internal architecture of the Calibre 7139 is derived from the base Calibre 7120 but represents a substantial divergence in terms of complication integration. Unlike modular perpetual calendars, where a module is simply stacked atop a base movement, the 7139 integrates the calendar functions to maintain a total thickness of just 4.1mm. This profile is achieved by merging the end-of-month cam with the date wheel and the month cam with the month wheel, a space-saving geometry borrowed from the RD#2 Ultra-Thin project. The movement operates at a frequency of 4 Hz (28,800 vibrations per hour), a higher beat rate than many ultra-thin perpetual calendars which often run at 2.75 Hz or 3 Hz. The higher frequency generally correlates with better rate stability and shock recovery, essential for a timepiece intended for daily wear.

The openworking process employed on the mainplate and bridges utilizes Electrical Discharge Machining (EDM). This process uses electrical sparks to erode material with micron-level precision, allowing for the creation of complex inner angles and skeletonized structures that traditional milling cannot achieve without inducing stress on the metal. Following the EDM process, the components undergo roughly 30 hours of manual finishing. The "V-angles"—internal angles where two chamfers meet—are hand-polished, as machine polishing cannot reach into these acute corners without rounding the edges. The aesthetic result is a movement that allows light to pass through the barrel and gear train, revealing the winding state of the mainspring and the motion of the pallet fork.

Mechanically, the Calibre 7139 is designed to address the long-term chronometry issues often associated with skeletonized movements. The removal of material from the bridges can theoretically reduce structural rigidity, leading to potential warping or misalignment of the gear train pivots. To mitigate this, Audemars Piguet has reinforced key stress points and utilized a non-magnetic balance spring. The balance spring is hand-fitted to the balance wheel, a procedure requiring specialized labor to ensure concentric breathing. The movement provides a minimum power reserve of 55 hours. While not an "extended" power reserve by modern 72-hour standards, it is sufficient to maintain timekeeping overnight and through short periods of inactivity, assuming the watch is kept on a winder for longer durations to maintain the calendar synchronization.

The patented crown correction system utilizes a complex arrangement of sliding pinions and levers. In position 1, the crown winds the mainspring. In position 2, it corrects the date and month. In position 3, it sets the time. A secondary position, denoted as 2’, meshes with the wandering wheels to adjust the additional calendar indications. This system negates the need for the wearer to carry a stylus, effectively modernizing the interaction with the complication. The system assumes a 122-year accuracy for the astronomical moon phase and requires no manual date correction until the year 2100, at which point the Gregorian calendar skips a leap year, a standard anomaly for mechanical perpetual calendars.

The Strap and Bracelet

The fitment of these timepieces adheres to the established design codes of their respective collections. The Code 11.59 is secured by a black alligator strap featuring large square scales, a hallmark of high-grade leather selection. It is paired with an 18-carat white gold triple-blade folding clasp. The clasp mechanism is skeletal in design, mirroring the openworked nature of the watch head, and is designed to sit flush against the underside of the wrist to minimize bulk. The lug width and attachment geometry appear standard for the Code 11.59 line, utilizing screw bars for security rather than standard spring bars, a necessary choice given the value and weight of the precious metal case.

The Royal Oak is fitted with its signature integrated bracelet, crafted primarily from titanium with BMG inter-links and studs. The use of BMG in the connecting studs is significant for wear resistance, as these articulation points are subject to constant friction and torque. The bracelet maintains the tapered profile synonymous with the Royal Oak, descending to a titanium AP folding clasp. The finishing on the bracelet requires a specialized calibration of the polishing wheels to ensure the transition between the titanium links and the mirror-polished BMG accents is seamless, as the two materials have different abrasion rates. The bracelet is integrated directly into the case via the double-plot system, ensuring the watch head sits balanced on the wrist despite the lightweight nature of the titanium.

Pricing and Availability

Audemars Piguet has listed the pricing for both the Code 11.59 Ref. 26443NB and the Royal Oak Ref. 26685XT as "Price on Request." This classification typically indicates that the models will be allocated exclusively through the brand's boutique network and AP Houses, with priority likely given to established clients with a documented purchase history of high-complication references. The production volume is constrained not only by the assembly time of the perpetual calendar mechanism but significantly by the bottleneck of the hand-finishing required for the openworked bridges.

The timepieces are covered by the manufacturer's standard two-year warranty against manufacturing defects. However, under the current "International Sales Warranty" program, registration of the timepiece allows for an extension of this coverage to five years. This extended warranty covers the proper functioning of the movement and water resistance, provided the user adheres to the service intervals recommended by the manufacturer. Prospective buyers should anticipate a significant waitlist period given the technical novelty of the Calibre 7139 and the collector demand for openworked Royal Oak derivatives.

Technical Specifications

Case: Code 11.59: 18k white gold bezel/caseback, black ceramic middle. Royal Oak: Titanium case, BMG bezel/caseback. Both 41mm diameter.

Movement: Selfwinding Calibre 7139; 29.6mm diameter, 4.1mm thickness; 4Hz (28,800 vph); 55-hour power reserve.

Dial: Sapphire dial with smoked external zones; openworked architecture; luminescent hands and markers (Pink gold accents on Royal Oak).

Strap: Code 11.59: Black alligator with 18k white gold folding clasp. Royal Oak: Titanium bracelet with BMG links and titanium folding clasp.

Price: Price on Request.

Reference Number: Code 11.59: 26443NB.OO.D002CR.01 | Royal Oak: 26685XT.OO.1320XT.01

Notes: All-in-one crown correction system; water resistant to 30m (Code 11.59) and 50m (Royal Oak); 5-year warranty upon registration.