French silver verge, astronomical deck watch Circa 1790

Silver deck watch with central seconds
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Very rare astronomical deck watch with central seconds by royal watchmaker Gregson, circa 1790.
A silver case with a high-quality five-part lateral hinge, extremely rare verge movement with central seconds and calendar. Originally signed enamel dial with a display of the date and the weekday as well as peripheral time indication, Movement intact.
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Diameter: 58 mm
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Weight: 45 g
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Signed:  Gregson  Paris