Introduced in 2001, the Patek Philippe Sky Moon Tourbillon ‘Ref. 5002’ was considered the most complicated wristwatch ever made – a timepiece that demonstrated Patek Philippe’s expertise in the art of watchmaking to the full. Not only are there an exceptional number of complications built into a watch with a case of just 38mm, but there is the highly novel second dial on the back face of the timepiece.

Starting with the ultra-light tourbillon, the two polished hammers minute repeating on two extra-long steel alloy ‘Cathedral’ gongs and a retrograde date display, there are a total of twelve complications in this extraordinary Patek. Meanwhile the dial on the back face of the watch boasts a counterclockwise-rotating disc which displays with incredible precision the starry sky and moon-phases of a specified location.

The estimate for this horological masterpiece is 840,000 to 1,200,000 euros. The auction will be held on 8 October in Hong Kong.

Photos: Sotheby's