French 18k gold watch with rock crystal back Circa 1920

Gold open faced pocket watch
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A very fine and very rare French, 18K yellow gold, a keyless pocket watch with rock crystal back to view the movement and unusual regulation lever, circa 1920. Sold to Monsieur Combes for 3,000 Francs. A polished case, reeded rims and band, the back glazed with rock crystal to view the movement, pendant and bow attached to the frosted gilt movement ring and detachable from the case.
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White enamel dial, radial Roman numerals, outer minute track and Arabic five-minute numerals, subsidiary seconds. Yellow gold Breguet hands. A frosted gilt movement, bar calibre, 17 jewels, counterpoised straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, index regulator with elongated arm, the tip protruding at the bottom of the case in a calibrated aperture. Dial signed.
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Diameter: 48 mm
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Signed: Breguet  Paris
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The use of rock crystal glazing in Breguet watches is very rare, although not unknown. Indeed, it recalls the legendary Breguet Marie-Antoinette, which had a rock crystal dial. In the present watch, the movement is visible and can be removed entirely from the case for servicing so that the rock crystal is not endangered. The regulation arm extends down through the bottom of the case.