Rolex. A gold automatic wristwatch, Ref. 3131, Oyster Perpetual Chronométre, ‘Bubbleback’, circa 1940.
Movement: automatic, patented Super Balance, no. 09296.
Dial: silvered, two-tone, Arabic and baton indexes, centre seconds.
Case: 14ct gold, screw-down back.
Signed: case, dial and movement.
Dimensions: diameter 32mm.
£3,000-£5,000

The Rolex reference 3131 was one of the first bubbleback models and features a two-piece rather than three-piece case. The auto-rotor movement with perpetual motion rotor was patented by Rolex in 1932 and the first of the bubbleback watches was launched the following year.