German double-sided astronomical watch with triple calendar Circa 1790

Silver double-dialled cylinder watch by Johann Rütger Ehrenberg
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An extremely rare German silver double-sided astronomical cylinder pocket watch with triple calendar, circa 1790. Cylinder escapement. Decorated white enamel dial on the front with decentralized time indication, Roman hours, outer minute divisions and front regulation, on the back also a white enamel dial with indication of the month (the number of days in this month), date and day of the week. Plain case, glazed on both sides. Movement signed.
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Diameter: 43.5 mm
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Weight: 74 g
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Signed: Joh. Roh. Ehrenberg à Elberfeldt
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Johann Rütger Ehrenberg was listed in Elberfeldt from about 1770 and died in 1815. The watch is considered to be possibly the most complicated watch known made by him and was formerly part of the Abeler collection.