Important English 18k gold lever precision watch Circa 1925

Gold lever with one minute tourbillon and 24h power reserve
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A very important, heavy English 18 carat gold precision pocket watch with one minute tourbillon and 24h power reserve indicator, circa 1925. Formerly awarded with a Kew A certificate. 3/4 Plate movement, optionally keywind or crownwind, chain/fusee, finely polished steel tourbillon cage of Nielsen type 1 with polished screws, English lever escapement with a counterpoised gold weight, Guillaume gold screwed compensation balance, freesprung blued balance spring. Silvered ground dial with Roman hours, subsidiary seconds and up and down indication. Plain case, casemaker’s punch mark RN for Robert Benson North, proprietor of North & Sons 1917-1933, successors to Nicole, Nielsen & Company, turning pendant. Accompanied by an Extract from the Archives and copy of the Frodsham records.
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Diameter: 58 mm
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Weight: 192 g.
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Signed: Chas Frodsham South Molton Stt London
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This watch was submitted for chronometer testing at Kew Observatory between March 2nd and April 15th, 1926.
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Charles Frodsham (1810-1871) was a maker of very fine watches, originally of the Strand, London and then New Bond Street. His best quality watches bear the letters AD.Fmsz, which is interpreted as 1850, the year he bought J.R. Arnold’s estate after his death, the firm was known for a short period as Arnold & Frodsham. He conducted many experiments with compensated balances and the balance spring to discover their underlying principles. He also wrote several papers on technical subjects.
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Robert Benson North (1867 – 1929) received his technical training at the British Horological Institute and won a number of prizes for both his theoretical and his practical work during his time at the institute. North accepted the position as Director and Manager of Nicole, Nielsen & Co. in 1898, in 1900 he became Managing Director of the company. Not only did North devote his experience and his skills to the company, in 1903 he also took out an important patent no 6737 for ‘Improvements in Revolving Escapements for Watches and other Portable Timekeepers’. Many of the firm’s most complicated high value watches were produced during that period of time. Nicole Nielsen & Co. were also famous for their collection of magnificent silver carriage clocks with tourbillon lever escapements. From 1905 on the company was known as North & Sons and Watford Speedometers. Robert Benson North was appointed Director and Chairman of Charles Frodsham & Co., Ltd in 1922. After North’s death in 1929, his son Robert Benson North took over his position in the company.