Thin French gold knife edged lever pocket watch Circa 1905

Gold open faced ladies’ watch
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A very small and thin French 18 carat gold open faced knife edged (montre couteau) keyless pocket watch made by Cartier in Paris, circa 1905. Very thin precision lever movement (2 mm). Original engine turned dial with Arabic hour numerals, outer minute divisions and blued Breguet hands. The case with white enamelled decoration on the back. Dial signed.
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Diameter: 32 mm
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Weight: 18.5 g
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Signed: Cartier Paris
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Normally, this kind of watch has a diameter of 45 to 50 mm.
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Couteau is the term used by Cartier in their manufacturing records to describe the type of ultra thin watches with knife edged cases, open faced or hunting cased models. These watches, with thicknesses of less than 4 mm for the open faced and less than 5 mm for the hunting cased version, are among the thinnest mechanical watches ever produced.
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For these thin watches from the first half of the 20th century, Cartier used movements from Edmund Jaeger (Jaeger-LeCoultre), who had just invented a movement only 2 mm thick. In the 1920s, Cartier and Jaeger formed a joint venture, the European Watch & Clock Co., whose signature can be found on many Cartier movements. Movements were further sourced from Vacheron & Constantin, who, from 1940, utilized a movement which was only 1.31 mm thick.