Swiss platinum doctor’s chronograph lever watch Circa 1920

Keyless dress watch with medical pulsometer 
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A fine and rare platinum keyless watch with chronograph medical pulsometer graduated for 30 pulsations and 30-minute register. Made by Paul Ditisheim, La-Chaux-de-Fonds Circa 1920. Three body bassine and polished case with a hinged back cover with engraved foliate monogram, semi concealed hinge and a co-axial button in the crown for start stop and return to zero functions of the chronograph.
Brushed silver dial with blue champlevé Breguet numerals, outer minute track and concentric fifths of a second divisions with Arabic five-second numerals, outer pulsometer scale graduated for 30 pulsations, subsidiary dials for the seconds and 30 minute register, inscribed above the seconds dial ‘Carlos U. Perret Rosarro’ and blued steel Breguet hands. Rhodium-plated movement with Geneva striping decoration, 21 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring and swan neck micrometre regulator.
Dial signed.
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Diameter: 45.5 mm
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Signed: Paul Ditisheim