Seen in the caseback, the oscillating mass in the movement is delicately engraved. It's made from eighteen-karat gold and decorated by hand with a barley grain sample, done by guilloche In case your Omega has the phrases 'Learn Chronometer' around the dial—as is viewed inside the Seamaster Diver 300M—you are https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/