German pocket watch with 36h power reserve indicator Circa 1939

Extremely rare gold open faced pocket watch by A. Lange & Söhne
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An extremely rare German gentleman’s pocket watch with 36h power reserve indicator, quality 1A, with original box, certificate and Lange extract from the archives, circa 1939.
14 carat gold case, design “Royal”, with gold dome. Signed gilt dial with Arabic numerals, auxiliary seconds and blued Éventail hands. Signed 3/4 plate movement, frosted, gilt, with screwed gold chatons, 20 jewels, gold screw compensation balance, index spring fine adjusting device, gold lever and chatoned diamond endstone on balance.
The up and down mechanism was developed by Otto Lange and was used in only five of Lange’s watches.
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Diameter: 53 mm
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Weight: 103 g
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Signed: A. Lange & Söhne Glashütte
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Sold for 935 reichsmarks on January 4, 1940 to Prof. Dr. C. Herglotz, Professor of Mathematics in Goettingen.