French watch, key with calendar and moon-phases Circa 1800

Gold watch together with a special gold key
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A French yellow gold open faced watch together with a yellow gold key with calendar and moon-phases circa 1800, gilt full plate movement, verge escapement, signed gilt dust cover.
White enamel dial, Roman numeral, polished case, movement and cuvette signed Tavernier à Paris, together with a yellow gold key, white enamel dial calibrated for date and day in French, the reverse with fan-form aperture for moon-phases, dial signed Le Tavernier.
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Diameter: 51 mm  Length of key: 42 mm
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Signed: Etienne Tavernier à Paris