Swiss gold open faced keyless chronograph Circa 1925

Gold doctor’s chronograph
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A very fine and rare Swiss 18 carat gold open faced keyless lever pocket watch with chronograph, 30 minute counter and pulsometer scale made by Longines in Saint-Imier, circa 1920. Rhodium plated movement with Geneva Striping decoration, 17 jewels, a straight line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring and an index regulator. The hinged gold cuvette engraved 5 Grands Prix – Paris – Anvers – Paris – Milan and prize medals. White enamel dial with black Roman hours, outer minute and fifth of a second track with red Arabic five minute numerals, an outermost red pulsometer scale graduated to 30 pulsations, subsidiary seconds at 6 o’clock, a 30 minute counter at 12 and gold spade hands. A solid, polished case. Dial, cuvette and movement signed, case numbered.
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Diameter: 53.5 mm
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Signed: Longines Chronometro Medical