Swedish experimental chronometer watch Circa 1850/1860

Open faced gold pocket watch by J.W. Grönbäck
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An interesting and unusual, rare Swedish chronometer with experimental movement, circa 1850/1860.
18 carat gold case with matching numbers on the case and movement. Very rare precision lever movement with chronometer balance and unusual construction, similar to Eppner calibre from the 1850s/60s, main plate signed and key winding. White enamel dial in excellent condition, featuring Roman numerals, a subsidiary dial with Arabic numerals for seconds, and filigree steel hands.
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Diameter: 48 mm
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Weight: 76 g
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Signed: J.W. Grönbäck Stockholm