Very early French gold anti magnetic chronograph Circa 1910

Gold anti magnetic lever chronograph with register 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 1910. Chronographe Ecran Paramagnétique. 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: 52 mm
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Signed: L. Leroy & Cie à Paris
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This watch is a very early anti magnetic watch, the first anti magnetic pocket watches were sold in 1915 by Vacheron & Constantin, though there had been some experimentation as early as 1846. This watch appears to pre-date those of Vacheron and shows that Leroy made anti magnetic watches very early. The watch is protected from magnetic fields by a soft iron band encircling the movement. The close-fitting cuvette inscribed ‘Paramagnétique’, probably made of tantalum, completes the movement’s protection.