Swiss 18k rose gold lever World Time dress watch Circa 1948

Rose gold World Time lever with short gold chain by Patek Philippe
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A very fine and very rare Swiss 18 carat rose gold keyless lever World Time dress watch with a short gold chain, circa 1948. Sold on December 13th, 1961. 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. Champagne-coloured dial with applied rose gold dot indexes and Roman quarter hour numerals, outer Arabic dark and light revolving chapter ring for day and night hours and the world time chapter ring, bearing the name of 41 locations around the world and revolving with the bezel according to the Louis Cottier world time patent, original gold circle and dauphine hands. Polished case with brushed back and milled revolving bezel. Dial, case and movement signed, case numbered. Accompanied by the original fitted box and the Extract from the Archives.
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Diameter: 44.5 mm
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Signed: Patek Philippe Genève
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Ref. 605 HU (Heures Universelles)
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The World Time system was invented around 1935 by Louis Cottier (1894-1966), a famous 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:
Ref. 515 a rectangular ‘galbé’ rose gold model made in 1937, with the names of 28 cities on the dial, the time differences between them based on Greenwich Mean Time. It is the earliest known, only three examples are known today.
Ref. 542 HU (Ø 28 mm), started around 1937, bears the names of approximately 30 cities on the revolving bezel. Only 4 examples are known to date. 
Ref. 96 HU Calatrava, with the names of 28 cities on the dial, appears to be a unique example made in 1939.
Ref. 130 of which only one example is known and was made on special order by Patek Philippe in 1939, is an 18 carat yellow gold mnemonic World Time chronograph wristwatch with square push buttons, register and tachometer. This watch does not have a World Time movement but features a World Time dial with the names of 24 cities. The time difference between the various cities is based on Berlin, which is at noon. 
Ref. 1415 HU began to be produced around 1939-1940. It has teardrop-shaped lugs, a 31 mm diameter and on the revolving bezel the names of approximately 30 to 41 cities. This model was produced in yellow gold with a silvered dial, in yellow gold with a cloisonné enamel dial representing various continents, in rose gold, with silver, champagne or pink dial, in rose gold, with cloisonné enamel dial representing various continents, in platinum with silvered dial.
Ref. 1416 HU is similar to Ref. 1415 HU and was produced at the same time, with the only difference being that it has straight ‘claw’ lugs. Three examples are known today. Ref. 1415-1 was created in 1940 for Dr P. Schmidt. This is a unique World Time chronograph wristwatch, in yellow gold, with square push buttons and the names of 33 cities.  
Ref. 605 HU was produced circa 1940-1960 and is a series of dress watches, with on the revolving bezel the names of approximately 30 to 41 cities. Some examples have a matte silvered or black dial and others have a cloisonné enamel dial.
Ref. 2523 HU and Ref. 2523-1 with two crowns, were produced circa 1953-1965. They bear the names of approximately 40 cities on the revolving bezel. They were made in rose gold, with silvered guilloché dial, in rose gold, with translucent enamel dial, in rose gold, with cloisonné enamel dial representing various continents, in yellow gold, with silvered guilloché dial, in yellow gold, with translucent enamel dial, in yellow gold, with cloisonné enamel dial representing various continents and one example is known to date in white gold, with cloisonné enamel dial representing various continents.