Accurate Swiss silver Chronometer precision watch Circa 1918

Silver watch with blue sapphire jewels
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An extremely accurate, Swiss silver keyless lever Chronometer precision watch with blue sapphire jewels, circa 1918. Guillaume balance, achieved 1st Class Bulletin de Marche from the Observatoire de Genève on February 27, 1919, régleur: H. Lossier. Accompanied by the original Bulletin de Marche. A polished case with a hinged silver cuvette. White enamel dial, radial Roman numerals, outer minute track, subsidiary seconds and silver spade hands. Rhodium plated movement, Geneva striping decoration, 18 jewels, the upper ones blue sapphire, stamped twice with the seal of Geneva quality mark, straight line lever escapement, Guillaume compensation balance with gold temperature and meantime adjustment screws, blued steel Breguet balance spring with a terminal curve, index regulator, wolf’s tooth winding.
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Diameter: 62.5 mm
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Signed: W. F. Schulz  Genève
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Accompanied by the original Bulletin de Marche
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The case and movement are signed W.F.S., movement numbered twice and case numbered. The present watch was sent for trial at the Observatoire de Genève between 30th December 1918 and 17th February 1919. It achieved a First Class Bulletin de Marche on 27th February 1919 with an extremely small variation over the testing period of only +0.90 of a second. The Régleur concerned was Monsieur H. Lossier. Being a watchmaker of such evident ability, it is surprising that no information can presently be found about W. F. Schulz. Being destined for Observatory Timing Contests, the movement of this watch, like those of other makers, was double engraved with the movement serial numbers.