Very unusual Swiss silver open faced keyless lever watch Circa 1910

Silver watch with 24-hour day and night dial
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A fine, rare and very unusual Swiss silver open faced keyless lever pocket watch, circa 1910. Matte gilt movement, 15 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring with overcoil, index regulator. A hinged silver cuvette engraved with prize medals. White enamel 24-hour day and night dial to Swiss patent No. 30613, the lower half in a darker tone to indicate the night-time hours, radial Arabic numerals 1-12 and 13-24, inner red supplementary numerals 1-12, an outer minute track, subsidiary seconds and blued steel Breguet hands, the hour hand making one full rotation in 24 hours. The case back is engine-turned with a central foliate cartouche, a polished gilded bezel, band and border. Dial and cuvette signed, case and movement signed and numbered, the case with Swiss and German silver marks.
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Diameter: 51 mm
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Signed: Omega