French gold anti magnetic chronograph with register Circa 1911

Gold keyless lever chronograph by L. Leroy & Cie
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A very fine, extremely rare and very early French 18 carat gold open faced anti magnetic chronograph keyless lever pocket watch with instantaneous 30-minute register, circa 1911. Frosted gilt movement, 21 jewels, straight-line lever escapement, cut-bimetallic compensation balance with gold and platinum screws, palladium Breguet balance spring, index regulator. Paramagnetic snap-on cuvette probably made of tantalum. White enamel dial with Breguet numerals, outer minute divisions, outermost fifths of a second chronograph divisions, subsidiary 30-minute register at 12 o’clock, subsidiary seconds at 6 o’clock and original gold spade hands. Polished case, the back with engraved monogram, the interior engraved temoignage de sympathie et de reconnaissance les mandataires et les acheteurs Janvier 1912, button for start/stop and return-to- zero of the chronograph in the crown, soft iron band surrounding the movement. Dial and cuvette signed, case numbered. Accompanied by the original Leroy fitted box.
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Diameter: 51.5 mm
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Signed: L. Leroy & Cie à Paris