Omega gents seamaster 300m chronometer watchsteel on steelchronometerdatehelium escape valvescrew in crownunidirectional rotating bezelcrystal domed scratch resistant sapphire crystal with anti reflective treatment on both sidescase steeldial blackwater resistance 300 m 1000 feetsize case diameter 41 mmmovement caliber omega 2500 self winding chronometer co axial escapement movement with rhodium plated finish power reserve 48 hours