Swiss pocket watch with hidden calendar on back Circa 1880

Rare gold open faced Ankerchronometer 
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A rare Swiss Ankerchronometer with hidden calendar on back, circa 1880.
18 Carat gold case, engine turned, “à goutte”, spring lid on back, rare calendar with week day and date indication, glazed movement. Ankerchronometer movement, finest quality, with wolf’s toothing and screwed gold chatons, calendar movement, big chronometer balance with gold screws, ring lever. White enamel dial with Roman hours, Arabic minutes, sunk subsidiary dial for the seconds and gold spade hands.
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Diameter: 51 mm
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Weight: 105 g
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Signed: No name