English gold lever with Bonniksen 52½ minute carrousel Circa 1900

Gold keyless lever by Bahne Bonniksen
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A very fine English 18 carat gold open faced keyless pocket watch with Bonniksen patented carrousel regulator, circa 1900. It obtained a Kew Observatory Class A Certificate, Especially Good, with a score of 80.9 marks. From the late James McCabe, Thomas Gammage & Son, 60 Queen Victoria Street in London. The case with London hallmarks for 1900-1901. A solid, polished case with master mark W.H. and a hinged gold cuvette.
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White enamel dial by Willis with radial Roman hour numerals, an outer minute track, subsidiary seconds at 6 o’clock and blued steel spade hands. A frosted gilt ¾ plate movement with 17 jewels, a going barrel, lateral lever escapement, free sprung cut bimetallic compensation balance with gold screws, blued steel Breguet balance spring with a terminal curve and diamond endstone, all mounted on a Bonniksen 52½ minute carrousel regulator. Dial inscribed with the rating details, movement signed by the retailer and punched with Bonniksen’s mark on the pillar plate.
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Diameter: 53 mm
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Signed: Bahne Bonniksen
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The case has some scratches.
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Bonniksen’s patent carrousel enjoyed particular success in the Kew Observatory trials. Kew Observatory trials for watches, various testing laboratories around the world were responsible for grading and testing watches. The most stringent is the Kew (Teddington) Observatory, just west of London. A standard Swiss chronometer test would last 15 days, however, the Kew test lasted 44 days. The tests consisted of observing the timekeeping of the watch in various positions and at various temperatures, and awarding points for accuracy in these differing states. 85.3 Marks are not a record breaking figure but are regarded as especially good (scores of over 90 were regularly obtained by 1900) and still do the makers great credit. The eight testing positions were as follows: Pendant up – 67°, Dial-up – 42°, Pendant right – 67°, Dial-up – 67°, Pendant left – 67°, Dial-up – 92°, Pendant up – 67° and Dial down – 67°