25668BA Audemars Piguet Perpetual Calendar Skeleton

The reference 25668BA is Audemars Piguet's Openworked Quantième Perpétuel in yellow gold, and the most expressive of a bloodline that begins with the 5548 of 1978. Where the 5548 introduced the thinnest self-winding perpetual calendar the world had seen to revive mechanical watchmaking in Switzerland, the 25668 stripped the movement bare and put it on display through both a skeletonized dial and a sapphire caseback. It is a watch more focused on drama than complication—but does both. The 36mm case, stepped bezel, and short downturned lugs were penned by Jacqueline Dimier, among her most assured work.

Photography for this Find comes via a prior sale by A Collected Man. 

That movement is the calibre 2120/2800, and its origin is the reason the reference matters. The ultra-thin 2120 base descended from a 1967 Jaeger-LeCoultre project that AP funded, later shared with Patek and Vacheron. The perpetual calendar module, however, was developed in secret during the quartz crisis by three senior AP men—Michel Rochat, Jean-Daniel Golay, and Wilfred Berney—who worked after hours, unpaid, fearing management would never sanction the spend. The result, at 3.95mm, was the thinnest perpetual calendar ever made. It is fair to argue that this calibre, not the Royal Oak, is what carried AP through the crisis.

Production dates deserve attention. Most sources, including AP-adjacent retailers, place the 25668's run from roughly 1988 to 1993, though some catalogue it into the mid-1990s and individual pieces surface dated 1989 and 1993. The totals are firmer: around 205 examples across all metals, of which just 94 were cased in yellow gold, the BA suffix. Against neo-vintage QPs that trade in the thousands, this is genuinely scarce, and the openwork references have always sat a step outside the collector spotlight. It differs from the earlier 25558 largely in case construction and extruded pushers. 

What justifies that rarity is time investment. Openworking here is not mere cutting away; it is hand engraving, bevelling, anglage, black polish, and a ridiculous run of inner angles, extended even to the skeletonized moonphase and the solid-gold rotor. Blued sword hands and champagne subdial rings supply the only warmth against all that work. The 25668BA is a reminder of the other AP—the one whose greatest contribution to watchmaking was made quietly, after dark, and is still too easily overlooked.