51mm Inside the case is the Oris Calibre 774, a slightly modified movement based on a Sellita SW-500 The Oris Dive Control Limited Edition was developed in partnership with Roman Frischknecht, a Swiss commercial diver who spends his working life deep underwater, servicing the subsea industry. https://www.oris.ch/en/watch/oris-dive-control-limited-edition/01-774-7727-7784-set