English precision lever with 12 minute tourbillon Circa 1902

Gold lever with tourbillon, carrousel and double roller escapement 
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An extremely rare, important English 18 carat gold open faced lever precision pocket watch with Robert Benson North‘s patented 12-minute flying tourbillon, carrousel and double roller escapement, circa 1902. Frosted gilt 3/4 plate movement, ébauche: Nicole Nielsen, frosted, raised barrel engraved with honour cyphers, gold chatoned centre wheel, gilt flying tourbillon frame, gold screwed compensation balance, chatoned diamond endstone on balance. Gold cuvette with dedication engraving: J.Z.H. from J.W. Xmas 1902. Off-white enamel dial with Roman numerals, auxiliary seconds and blued spade hands. Plain case, turnable pendant, case maker’s punch mark H.M.F. for Harrison Mill Frodsham. Dial and movement signed and numbered. Accompanied by a Frodsham certificate and copies of Kew Observatory Extracts from the Archive.
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Diameter: 58 mm
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Weight: 198 g
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Signed: Chas Frodsham
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This piece was twice submitted for testing at Kew Observatory and achieved 80.3 points in the final test.