Noticeable throughout the caseback, the oscillating mass with the movement is delicately engraved. It is actually made out of eighteen-karat gold and decorated by hand using a barley grain sample, finished by guilloche The Diver 300M is obtainable in steel or mixtures of steel and yellow or Sedna gold, by https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/