GOLD ROLEX BUBBLE-BACK REF. 3131, 40S Three body tonneau Oyster 14K gold case, concave lugs, slopped bezel, screwed back marked Rolex and RWC (Rolex Watch Co) Ltd, screw-down crown. Not original strap and gold Rolex buckle.
Silvered dial signed, "Officially Certified Chronometer”, printed crown logo, applied arrow and arabic indexes, outer minute and 1/5th second divisions. Gold feuille hands, centered seconds.
Signed self-winding movement, nickel-finished caliber 630 Chronometer, n. 71286, 17 jewels, indirect seconds, lever escapement, Super Balance adjusted to seven positions, blued Breguet hairspring.
Diameter Ø: 32 mm 
Note: working, but a servicing is suggested; original Rolex+Oyster crown as spare part.