Swiss staybrite steel keyless lever chronograph Circa 1935

Staybrite steel chronograph with register by Zenith
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A fine Swiss staybrite steel open faced chronograph keyless lever pocket watch with 30 minute register, circa 1935. Brass plated movement, 21 jewels, straight-line lever escapement, cut bimetallic balance with self compensating blued steel Breguet balance spring, spring loaded micrometric regulator. White enamel dial with black Breguet numerals, outer minute and seconds divisions with red five minute Arabic numerals, subsidiary seconds, 30 minute register below 12 o’clock and original gilt spade hands. Polished case, snap-on steel cuvette. Dial, case and movement signed, case numbered.
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Diameter: 51 mm
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Signed: Zenith