Audemars Piguet Royal Oak QP Perpetual Calendar ref 25554BA

The reference 25554BA: the very first Royal Oak to feature a perpetual calendar. Just 0.4mm thicker than the ultra-thin ref. 5402, it’s an engineering marvel, AP fit the Quantième Perpétuel cal. 2120/2800 into nearly the same case with only minor adjustments.

Nerdiness aside, it’s simply a gorgeous watch. Cream dial, 18k yellow gold case, and all the finishing the Royal Oak is known for.