Steel chronograph lever watch with pulsation scale Circa 1920

Unusual open faced chronograph by Rolex
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An unusual Swiss stainless steel open faced keyless lever chronograph watch with pulsation scale, circa 1920. Nickel finished jewelled lever movement, bimetallic compensation balance. Two toned silvered dial, central polished time dial with Arabic numerals, outer calibrated red and black pulsation scale, two engine turned subsidiary dials for 30 minute register and constant seconds. Hinged case back, chronograph operated through one button in the crown. Dial and movement signed, case signed R.W.C. Inc., case numbered.
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Diameter: 49.5 mm
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Signed: Rolex Marconi