Unusual stainless steel flyback split chronograph Circa 1940

Unusual open faced chronograph watch by Longines
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An unusual Swiss stainless steel open faced keyless flyback split chronograph watch, circa 1940. Mechanical movement, 19 jewels, gold anti magnetic pallets. Hinged steel cuvette. White enamel dial with Breguet numerals, Arabic five minute divisions, two subsidiary dials for constant seconds and 30 minutes register. Plain case, hinged back engraved Austin Mc Laughlin, two round chronograph buttons in the band, the first at 11 for start/stop functions, the second at 1 for split seconds functions, reset function through a coaxial button in the winding crown. Case, dial and movement signed.
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Diameter: 52 mm
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Signed: Longines