Visible in the caseback, the oscillating mass of the motion is delicately engraved. It's produced from eighteen-karat gold and decorated by hand which has a barley grain sample, finished by guilloche A paragon of robustness and trustworthiness, the 40 mm Oyster case of the new GMT-Grasp II is guaranteed waterproof https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/