Swiss bagnolet calibre thin watch with visible movement Circa 1840

Gold extra flat watch with gold chain and brass male key
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A very fine and rare 18 Carat gold extra flat watch with bagnolet calibre and visible movement,  accompanied by an 18 Carat gold chain and brass male key. Made by Edward Robert Theurer in La Chaux-de-Fonds, Switzerland, circa 1840. Three body and bassine pincée case with engine-turned back cover with a female aperture for winding.
White enamel dial with an annular ring with radial Roman numerals and outer minute track and blued steel Breguet hands. Single gilt brass movement with foliate engraved plate, 8 jewels, bar calibre with foliate engraved bridges, plate and barrel, cylinder escapement, three-arm brass balance with flat balance spring and an index regulator.
Movement signed, case numbered.
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Diameter: 44.5 mm
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Thickness (with glass): 5 mm
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Signed: Edward Robert Theurer