Limited to just 50 pieces, this is one of the most investment worthy Royal Oak's for sale today. Released in 2010, this rare grand complication is the first AP Offshore Tourbillon with Chronograph ever produced; the result of nearly a decades worth of R&D. Last published retail price was $299,300.

Anodised aluminium bridges suspend the tourbillon at 9 and the twin main spring barrels (both feeding into the balance simultaneously). The true masterpiece though is the hand-wound calibre 2912 with a massive 237 hours of power-reserve, exclusive to this 1st series.

One of the reasons that so few watches are long-duration like this ten-day piece, is the required specialist knowledge to precisely control the amount of power in such a long mainspring. For this Royal Oak 26288OF, Audemars Piguet have reverted to a device called Geneva Stopwork.

When wound, this device, a pronounced point on the gear (visible in our photos on the barrel near 5) goes round once for every day of running. When the 10th day comes round, this finger abuts a solid stop piece geared to it, blocking any further motion. The stopwork saves the watch from over-winding, and it also makes sure that the weakest part of the mainspring is never used – this helps keep the amplitude of the balance stable for the entire duration of its 10 days; an impressive feat in horology. Curiously, this details has been seldom mentioned in publications. 

The large 44mm rose gold case is typical of the Royal Oak Offshore, with crisp edges to the finishing and perfectly milled triangular cut-away. For the winding crown & oversized Chronograph pushers, AP have utilised exotic materials; a forged pressed carbon fibre bezel, and ceramic for the winding crown and pushers. Fitted to a black alligator strap, secured by its 18ct rose gold AP deployant buckle, and waterproof to 100m.

Like any important watch, it's accompanied by its large wooden locking Audemars Piguet display box and its AP warranty book, retailed in Istanbul 2014. Guaranteed for two years.