Swiss ultra-thin gold and platinum keyless watch Circa 1918

Gold lever watch by Audemars Piguet 
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A fine ultra-thin yellow gold and platinum open faced keyless watch, circa 1918. Keyless manual winding movement, 19 jewels, silvered dial with painted black Arabic numeral, subsidiary dial for constant seconds,  platinum and yellow gold case, snap-on case back embodied with a pink gold initial “H.C.M”, dial and movement signed, case numbered.
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Diameter: 43 mm
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Signed:  Audemars Piguet  Genève