1. Royal Oak RD#2 Perpetual Calendar Ultra-Thin by Audemars Piguet
Audemars Piguet (AP) really outdid itself with this one. By breaking with traditional thinking and embracing simplification, AP reduced its perpetual calendar from a three-level movement, where the wheels and gears were layered upon one another, to one with a single flat mechanism, where all the components are working together cohesively rather than independently for each of the functions.
At 6.3mm, AP has created the thinnest perpetual calendar watch the world—a true tour de force from the manufacture in Le Brassus. Unfortunately, this piece is a concept watch and not available for sale, but if and when it does become available, there will certainly be a long waiting list.