The thinnest mechanical watch in the world, the Piaget Altiplano 900P is given a pair of red hands to create the unique edition for Only Watch 2015.

Introduced two years ago, the Altiplano 900P is the thinnest wristwatch on the market, standing just 3.65mm high, case and all. For Only Watch 2015, Piaget has added a dash of colour to the Altiplano 900P with the hour and minute hands in bright red. The 900P manages to be so thin thanks to its unusual movement that combines the movement and the case, an idea originating in the ultra-thin Jean Lassale movement of the 1970s and now found only in quartz watches. Instead of a base plate as the foundation of the movement, the gears of the movement are mounted onto the case back, eliminating the height of the base plate in a conventional movement.

And the escapement and gear train and laid out around the dial, rather than underneath it, further shaving off the millimetres. This construction has the advantage of giving life to the dial, which shows the balance and escape wheels in constant motion, in contrast to the typical ultra-thin timepiece that is entirely static.

The Altiplano 900P Only Watch edition is also engraved as such on the case back.

Only Watch 2015 takes place on November 7, 2015 in Geneva. A total of 43 watches (see the rest of them) will be sold, with all proceeds going towards research into Duchenne muscular dystrophy.