Visible with the caseback, the oscillating mass from the motion is delicately engraved. It's constructed from 18-karat gold and decorated by hand using a barley grain sample, performed by guilloche William’s charting, aided because of the H4, effectively predicted landfall at Kingston within a margin of an individual nautical mile- https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/