German silver lever deck watch with power reserve Circa 1940

Silver keyless pocket chronometer by A. Lange & Söhne
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A fine German silver open faced keyless lever deck chronometer destined for observatory trial with power reserve indication, circa 1940. Frosted gilt 3/4 plate movement with separate bridge for the escape wheel, engraved twice with the movement number, 17 jewels, straight-line lever escapement with lateral banking extension on the entry pallet, Guillaume type balance modified by Lange, blued steel Breguet balance spring with patent stud fastening, index regulator. Hinged silver cuvette. Brushed, silvered dial with painted black Arabic numerals, outer minute track, large subsidiary seconds at 3, power reserve indication at  and original blued steel spade hands. Polished case, the back engraved with the movement number. Case, cuvette and movement signed, movement numbered.
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Diameter: 60 mm
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Signed: A. Lange & Söhne Glashütte i/SA