Visible through the caseback, the oscillating mass from the motion is delicately engraved. It's comprised of eighteen-karat gold and decorated by hand by using a barley grain pattern, accomplished by guilloche In case your Omega has the words 'Master Chronometer' on the dial—as is viewed during the Seamaster Diver 300M—it https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/