These skeletonized Royal Oak Perpetual Calendars are as rare as they are cool. Audemars Piguet reports that only 126 examples of link the ref. 25636 were ever produced in yellow gold, with even less – reportedly just 34 examples – in platinum. Pharrell has 'em both.The platinum example is lot 22 in the auction and has a pre-sale estimate of $125,000 - $250,000, while the yellow-gold RO is lot 19 and has an estimate of $100,000 - $200,000.