Greubel Forsey

Double Tourbillon 30° Robert Greubel and Stephen Forsey's first invention puts one tourbillon inside another. The inner cage, holding the balance and spring, is tilted at 30 degrees and turns once a minute, while the outer cage turns once every four minutes, so the watch averages out gravity's effect across more positions than a flat tourbillon can. Made from 2004 to 2010 in a run of 144 pieces, it announced a workshop that treats the tourbillon as a research problem rather than an ornament, and its finishing set the standard the partners have kept to ever since.