This Cosmos Perpetual Calendar Royal Oak 25820ST features a striking combination of the iconic Royal Oak case, an unusual indigo blue dial and a perpetual calendar movement central to the manufactures history. Housed in stainless steel, it embodies much of the spirit and innovation which carried Audemars Piguet forward in the second half of the 20th century.

A Perpetual Calendar Royal Oak

Its been almost 50 years since the creation of the original and this now classic piece, is more popular than ever. First unveiled by Audemars Piguet in 1972 and designed by , who incidentally designed the Patek Philippe amongst others, the Royal Oak has become a cultural icon, due to its distinctive features and its role as a pioneer for high-end luxury sports watches.

The first Royal Oak to feature a perpetual calendar complication was released in 1983, as the reference 5554 (later designated the ref. 25554). At the time, the combination of the sporty, Royal Oak case and complicated perpetual calendar movement was an unusual, forward-thinking approach by the brand.

A canvas for experimentation

Since its introduction, Audemars Piguet has used the Royal OakPerpetual Calendaras a canvas to experiment with different metal combinations and dial designs. From the tantalum two-tone examples to openwork dials, the collection offers a rich variety of configurations, where the manufacture has pushed the boundaries of conventional design.

This example, with its deep blue dial, speaks to that approach. This seldom seen, navy blue tone is noted as "Blue Cosmos" on the accompanying Archive Extractfrom Audemars Piguet, with an additional.05 dial code at the end of the reference number. Evidence suggests the dial was manufactured by Stern Creations, the famed manufacturer of dials, which also made dials for the original Royal Oak ref. 5402.

The Design

The layout of the dial includes all the traditional indications of a perpetual calendar: day, date, astronomical moon (with graduation for moon age) and month. It features original luminous-filled baton hands, a feature typically found in Royal Oak watches, where the index markers are also luminous. The sub-dials are slightly recessed, giving the dial greater depth and texture. It features the "Audemars Piguet" signature in the more modern lettering, adopted by the brand towards the end of the millennium.

It retains the more understated Grande Tapisserie pattern, forming the square and lozenge motif, as seen in earlier executions of the Royal Oak. Some newer versions of the Royal Oak have since adopted APs bolder Tapisserie Evolutive dial pattern, less faithful to the original design. The deep indigocolour is complemented by crisp white indications used throughout the dial.

The stainless case and bracelet are excellently finished, with angular, beveled and polished edges - striking the perfect balance between utilitarian function and elegant design. The polished screws, bezel and case edges fantastically-contrast with the brushed surface of the case and bracelet. At 39mm in diameter, and only 9.3mm thick, this Royal Oak Quantime Perptuel case sits comfortably on the wrist. On the reverse, the outer-case back correctly displays the unique serial number (E-73XXX), along with its case number (3XX).

The Movement

This Royal Oak Quantime Perptuel is powered by the AP caliber 2120/2800, derived from s legendary ultra-thin JLC 920 calibre movement. The caliber 2120 was an initial project of Jaeger LeCoultre in 1967, funded and contributed by Audemars Piguet, and famous for its adoption by Audemars Piguet, and .

The ultra-thin automatic 2120/2800 calibre features 38 working jewels, Gyromax balance and four ruby wheels to support the full-diameter rotor, which runs on a beryllium rail for stability. The AP calibre 2120 remains the thinnest full-rotor self-winding movement in the world, considered by many as one of the most technically refined wrist-watch movements ever made.

The Set

This Royal Oak 25820ST is accompanied by its original outer box, inner winding box, instruction manuals, setting pin and an Extract from the Archives, which confirms the watchs case, movement and serial number, as well as register date as June 2003.

Closer look