Noticeable throughout the caseback, the oscillating mass with the movement is delicately engraved. It's comprised of 18-karat gold and decorated by hand using a barley grain sample, carried out by guilloche William’s charting, aided through the H4, correctly predicted landfall at Kingston in a margin of an individual nautical mile- https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/