Calibre 2236 Is equipped using a Syloxi hairspring that is produced by Rolex and patented. This silicon hairspring contains a patented geometry that assures the calibre’s regularity in any place. In addition to his colleague Thomas Earnshaw, the pair would establish simplified and practical marine chronometers. The President bracelet from https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/