English precision watch with one minute tourbillon Circa 1910

Gold open faced watch with original box
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An important, heavy gold precision pocket watch with one minute tourbillon with original mahogany box with mother of pearl inlay, circa 1910. 18k gold case, tiered, polished, case maker punch mark “AB”, glazed movement, turning pendant.
Silvered dial, radial Roman numerals, auxiliary seconds, 36h power reserve indicator, signed, numbered, blued spaed hands.
¾ plate movement, frosted, gilt, chatoned, engraved barrel: “To H. M. The King of Spain”, chainee/fusee, Swiss lever escapement, Guillaume gold screw compensation balance with platinum regulation screws, finest mirror-polished tourbillon steel cage of Nielsen type 1
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Diameter: 57 mm
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Weight: 170 g
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Signed: S. Smith & Son, London