Swiss gold open faced lever chronograph watch Circa 1910

Chronograph with 15 minute recorder, tachometer and telemeter by Omega
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A fine, very rare Swiss 18 carat gold open faced chronograph keyless lever pocket watch with 15 minute recorder, tachometer and telemeter for 1 to 5 minutes base, circa 1910. Gilt brass 3/4 plate movement, straight-line lever escapement, cut bimetallic balance, blued steel Breguet balance spring, swan neck micrometer regulator, chronograph functions by a single button on the winding crown. Gold cuvette. White enamel dial with printed Arabic numerals, 1/5th seconds chronograph scale with 5 minute/second markers, sunk 15 minute register at 12, outer tachometer and 5 multicolor telemeter scales and original gold spade hands. Plain case, hinged case back and bezel, centre of the back engraved with a large T in a circle filled with blue enamel. Dial and case signed.
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Diameter: 53 mm
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Thickness: 16 mm
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Signed: Omega Cadran Breveté S.G.D.G.