Review: Audemars Piguet Royal Oak RD#2 Ultra Thin Perpetual Calendar

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A new ground breaking concept watch from Audemars Piguet, breaking all records for thinnest automatic perpetual calendar movement as well as thinnest automatic perpetual calendar watch at the same time. Boasting of very impressive height of only 6.3mm in a very wearable 41mm case, with the movement a mere 2.89mm high! Cased in a magnificent platinum case with bracelet. But we are ahead of ourselves. Presenting our detailed review of the Audemars Piguet RD#2 Ultra Thin Perpetual Calendar.

As we described in the Chief Editor’s Top 5 Choices, the AP Royal Oak RD#2 looks like any other Royal Oak…one with a Perpetual Calendar. Only when one examines the hefty platinum case does one realise that the 41mm watch is ultra thin. So thin that its case is thinner than AP’s own RO Jumbo Extra Thin which is 8.1mm high. The RD#2 measures 6.2mm, allowing it to claim the title of the world’s thinnest automatic perpetual calendar. For both the movement and the watch fully encased breaks the previous record.

The thinnest automatic perpetual calendar prior to this was held by two watches. One for the case and the other for the movement. The Vacheron Constantin Overseas Ultra Thin Perpetual Calendar’s case was the thinnest at 8.1mm thick. But its movement, the VC C.1120 QP is 4.01mm. The Patek Philippe Ref. 5490 at 8.48mm case height, but its the movement was the thinnest until now. The Patek C.240Q measures 3.8mm high. The The Audemars Piguet RD#2’s Royal Oak case handily beats both of them at 6.3mm high with a movement measuring a scant 2.89mm thick. Impressive specifications indeed.



The Audemars Piguet Royal Oak RD#2 Ultra Thin Perpetual Calendar


The first AP concept watch was given the moniker RD#1 in 2015. This was the AP Royal Oak Concept SuperSonnerie which we elaborated at length in this article here. In AP-speak, Concept is a collection line, and not an indication of the status of the watch being experimental and to showcase proof of concept. The designation RD is used for this. And an RD watch is a concept watch in the traditional sense of the word, and not to be sold. Only 5 prototypes of the RD#2 were presented in SIHH. But we can be sure the technology will trickle down to new watches soon.


Audemars Piguet Royal Oak RD#2 Ultra Thin Perpetual Calendar

But all these wizardry is useless if the watch does not perform reliably, nor if the proportions are out of whack. In our hands-on sessions with the RD#2, we found all indications that the RD#2 is robustly conceived and built. The proportions of the watch is so cleverly chosen, that it looks like any other Royal Oak.




The Case, Dial and Hands

The case is the classical Royal Oak case. Chandi Gruber, Head of Product Management told Deployant that as the movement is extremely thin, it is certainly possible to make the case thinner than the 6.3mm that it is. But in her opinion, that would compromise the proportions of the 41mm diameter Royal Oak case they have decided to put the new movement in. And at 6.3mm, it handily beats the record for thinnest automatic perpetual calendar watch, so it sufficed.


The case thickness of only 6.3mm. IThis is thinner than AP’s own RO Jumbo Extra Flat (8.2mm) and even thinner than the quartz RO 33mm.


And indeed, in the flesh (or in the metal), it stands this test of proportions very well. Without placing it side by side to a regular RO Jumbo, one is hard pressed to be able to identify that this is way thinner. All the classical RO case aesthetics of juxtapositioning polished and brushed surfaces are present.


Audemars Piguet Royal Oak RD#2: ultimate thinness in an automatic perpetual calendar watch. The case thickness is only 6.3mm but the proportions are so well chosen, that the watch looks right.


The dial too is classic Royal Oak, with the mini-tapisserie pattern. The pattern is done in-house in the AP facility in Le Brassus, and we will bring you a detailed report on how this is done soon. The pattern is not stamped, but is done by a computer controlled machine which immitates the exact movements of the traditional rose engine used for guilloche. And because it is computer controlled, the tolerances and replicability of each dial, and the ultimate quality can be managed to a degree much more precise than a  traditional machine will be able to do. AP designed and had these machines built to their specifications and is the currently the only facility capable of making guilloche dials in a semi-mass production.


The Audemars Piguet Royal Oak RD#2 Perpetual Calendar Ultra-thin.


The markings on the perpetual calendar are complex, as it includes all the classical indications – day, date, month, moonphase, power reserve  and leap year indicators. The layout is not cluttered in the dial, and remains quite legible.

The watch was presented in a solid platinum bracelet in the classical Royal Oak design. The stuff of legends, so many observers say. In the 70s, when it first appeared, it was made by Gay Freres, who was one of the top bracelet makers of the time. Gay made bracelets tor Heuer, Rolex, Universal Geneve, JLC, Patek Philippe. Gay Freres was purchased by Rolex in 1998.

The RO bracelet is made of component links which are all different in size, each brushed with polished edges. Not only does each link take a long time to prefect, but the bracelet has to be hand-assembled by an expert. The resulting fit and finish is quite spectacular.


The Movement: Caliber 5133

The innovation and technical wizardry goes beyond the ultra slim aesthetics. AP describes in its literature that this feat is akin to collapsing a 3 storey building into a single storey while keeping all the functions and a similar footprint. Though we think its more like collapsing 4 layers of a standard automatic perpetual calendar into two. Two layers remain, as full sized rotor counts as layer 1, and the rest of the movement as layer 2. But of course, the rhetoric of 3 into 1 sounds way more sexy.

AP movement designers chose to lay the movement out wider than to stack it up. As a comparison, the C.5133 measures 32mm in diameter, compared to the AP C. 5134 which is 29mm. The designers also simplified the movement. The C.5133 has 256 components vs 374 in the C.5134.


The sapphire caseback reveals the movement C.5133.


Technical details remain quite difficult to come by, as understandably, AP is rather secretive about the innovations. We were briefed about the innovative features in the Lab Room at the AP SIHH booth, and though there were models which explained how the new perpetual calendar worked, we were not allowed to take photographs.

Here is  our understanding of the work required to collapse stories of the house, so to speak. AP simplified the perpetual calendar, dropping the component count from the earlier perpetual calendar by AP. They did this by using a single 48 tooth month wheel for the 4 year leap year cycle. In a typical perpetual calendar watch, this is achieved with a 12 tooth month wheel, with a separate 4 year cam for the Feb to allow it to work for the leap year. But in the C.5133, this is a single wheel is programmed to account for all the 31-day months, 30 day months and the 28 or 29 day February months. The wheel is cut with notches where the deeper the depression, the shorter the number of days in the month. And as each month is represented 4 times on the wheel, it is able to account for the leap year February simply by having the non-leap year February cut to show 28 days, and a February notch which is less deep than the others for the leap year to account for 29 days. This simplification allowed a thinner calendar module to be made.

Another technique AP used to make the movement thinner is to use the dial as the support for the movement, effectively functioning as a plate. A hanging barrel is used, also to make the movement thinner. AP does not confirm, so we speculate till they release further information. We think this is similar to the technique AP used to develop the Ultra Thin Automatic Tourbillon C.2870 released in 1986. While the C.2870 used the case back as the rear plate, we suspect the dial of the C.5133 serves a similar function.

From the view through the sapphire caseback,  the movement finishing is very traditional haute horlogerie, meaning that it is performed to a very high degree. All the standard finnissage detailing is done to perfection – anglage, perlage,  Côtes de Genève, et al.

Currently the Audemars Piguet RD#2 is a concept prototype, only 5 examples have been made, and none currently available for sale. AP will use the prototypes as a model to trickle down to other watches, and we certainly are looking forward to seeing this ultra thin know-how soon.

As such, we will leave out the Competitive Landscape for this review. There is no competition, not only because the RO RD#2 is not for sale, but also there is no Automatic Perpetual Calendar watch which is ultra thin, automatic, and cased in a sporty case.


Concluding Thoughts

In conclusion, we find the Audemars Piguet Royal Oak RD#2 Ultra Thin Perpetual Calendar to be a very compelling proposition, if it were to be offered for sale. But as it is, it is an exploration on what AP can do, and it is indeed very impressive. We are certainly looking at the technology and savoir faire to trickle down into watches which are created for the market.


On the wrist, the heft and the thinness is certainly a well appreciated feature. And the 41 mm case slips under a bespoke shirt cuff easily, and looks very elegant.

Audemars Piguet Royal Oak RD#2 Ultra Thin Perpetual Calendar Technical Specifications

Movement: Selfwinding manufacture Calibre 5133

Total diameter 32.00 mm (14 ¾ lignes) Total thickness 2.89 mm Number of jewels 37 Number of parts 256 Minimal guaranteed power reserve 40 h Frequency of balance wheel 2.75 Hz (=19,800 vibrations/hour)

Case: 950 platinum case, glareproofed sapphire crystal and caseback, water-resistant to 20 m, RD#2 engraved on the caseback

Dial: Blue dial with “Grande Tapisserie” pattern, blue counters, white gold applied hour-markers and Royal Oak hands with luminescent coating

Bracelet: 950 platinum bracelet with AP folding clasp

Functions: Perpetual calendar with day, date, astronomical moon, month, leap year, night and day indication, hours and minutes

Reference: 26586PT.OO.1240PT.01



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