Seen through the caseback, the oscillating mass in the motion is delicately engraved. It is made out of 18-karat gold and decorated by hand using a barley grain pattern, done by guilloche A paragon of robustness and reliability, the 40 mm Oyster case of The brand new GMT-Grasp II is https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/