The Sidérale is an incredibly complex wristwatch, the most complex IWC has ever made. It combines a perpetual calendar and astronomical display with a (huge) constant force tourbillon. The oversized tourbillon, which displays running seconds, guarantees a regular and precise rate for a period of at least 48 hours, though the watch has a complete 90 hour power reserve. While the tourbillon may be the most immediately gratifying aspect of the Siderale, it is the caseback, with a color-changing star chat that is really the star of this show. It isn’t just a star chart on the back of the Sidérale, it actually displays for sunrise/sunset and coordinates of chosen location.