Extremely rare Swiss gold World Time dress watch Circa 1948

Gold lever with a map of the world dial
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A very fine and extremely rare Swiss 18 carat yellow gold keyless lever World Time dress watch, circa 1948. Sold on May 26, 1956. Rhodium-plated movement, Geneva striping decoration, 18 jewels, straight-line lever escapement, cut bimetallic compensation balance adjusted to heat, cold, isochronism and five positions, blued steel Breguet balance spring with swan-neck micrometre regulator. Polychrome cloisonné enamel dial that represents a planisphere map of the world, applied yellow gold hour indexes, outer Arabic dark and light revolving chapter ring for the day and night hours and World Time chapter ring, bearing the name of 41 locations around the world, revolving with the bezel according to the Louis Cottier World Time patent, yellow gold hands. Solid, polished case with satiné back, milled revolving bezel. Dial, case and movement signed. Accompanied by an Extract from the Archives.
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Diameter: 45 mm
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Signed: Patek Philippe Genève
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The World Time system was invented around 1935 by Louis Cottier (1894-1966), a well-known independent watchmaker in Geneva. This World Time system was used by Patek Philippe and by other major names in the Swiss watch industry, such as Agassiz, Rolex and Vacheron & Constantin. Patek Philippe created various series of World Timers from 1937 to the mid-1960s.