Ref. 2523 and Ref. 2523-1Patek Philippe World Time wristwatches, with two crowns,are Ref. 2523 HU (Heures Universelles) and production began in 1953.The two crowns have separate functions: the crown at3 o?clock adjusts the hands and the 24-hour ring; while the crown at 9 o?clock operates the disc with the names of 41 cities in the world.Production of the first series of the Ref. 2523 began in 1953 with7 examples in pink gold, of which 4 were with cloisonné enamel dial.Production was continued, with the Ref. 2523-1, in small quantities until the mid-1960?s, and these models were only made in yellow gold, white gold and pink gold, though the exact numbers for each are difficult to establish.The lugs of the 1950?s series are more prominent than those of the 1960?s series, which are somewhat flattened.This series features different types of dials:? matt silvered.? guilloché (or engine-turned), either on silver dial plate or on gold dial plate.? enamelled, such as blue translucent enamel.? polychrome cloisonné enamel representing a map of North America, or South America, Eurasia or Europe.Poinçons de GenèveThe voluntary quality control of watches at the Geneva Observatory, was established by a law dated November 6, 1886. Conditions were laid down for the attribution and stamping of the Poinçons de Genève, punch-marks designed as the coat-of-arms of Geneva. Pocket watches, or wristwatches which carry the Poinçons de Genève, considered as an equivalent to a Bulletin Officiel de Marche, punched on a bridge and on the main plate of the movement, were qualified to be officially termed ?chronometers?.The World Time system was invented around 1935 by Louis Cottier (1894 - 1966), famous independent watchmaker in Geneva. This World Time system was used by Patek Philippe and also by other major names in the Swiss watch industry, such as Agassiz, Rolex and Vacheron Constantin.Patek Philippe created various series of ?World Timers? and the earliest known is a probably unique rectangular ?galbé? pink gold model, Ref. 515, made in 1937, which was sold by Antiquorum, Geneva, April 10, 1994, lot 502, for SFr. 550'000 (US$ 388,560).From 1937 until about 1940, Patek Philippe used the ?World Time? movement in various types of cases:Ref. 542 (Ø 28 mm.), of which only 4 examples are known to date and three were sold by Antiquorum:- Geneva October 17, 1993, lot 431, at SFr. 121?000(US$ 81,700).- Geneva, October 15-16, 1994, lot 608, at SFr. 110'000(US$ 87,300).- Geneva, April 10, 1994, lot 500, at SFr. 231'000(US$ 164,200) with unusual bezel and hands.Ref. 96 Calatrava, which appears to be an unique example, made in 1939.Around 1939-1940 began the production of the series Ref. 1415 (drop-shaped lugs), together with three examples of theRef. 1416 (straight ?claw? lugs), both references with a diameter of 31 mm. and on the revolving bezel the names of 30 cities of the world.In 1940, Patek Philippe created, specially for Dr. P. Schmidt,a unique ?World Time? chronograph (Ref. 1415-1) wristwatch, in yellow gold, with square push-buttons and the names of33 cities of the world, which was auctioned by Antiquorum, Geneva, October 15-16, 1994, lot 516, setting a World Record at SFr. 990'000 (US$ 785,714). This watch is illustrated on the front cover and p. 270 of the new edition (1998) of Patek Philippe Wristwatches, by Martin Huber & Alan Banbery.From 1940 onwards, Patek Philippe produced ?World Timers?in three main series which include dress watches (Ref. 605, circa 1940-1960?s), some with a matt silvered dial or black dial and others with a cloisonné enamel dial; and, wristwatches, with one crown (Ref. 1415, circa 1939-1950?s), and two crowns (Ref. 2523 and Ref. 2523-1, circa 1953-1965), some with a matt silvered or gilt dial, some with a guilloché dial, some with an enamel dial and some with a cloisonné enamel dial. On the revolving bezel of the Ref. 1415; the name of 41 cities of the worldOn the revolving ring dial of the Ref. 2523; the name of 40 cities of the world.World Time Patek Philippe wristwatches are published in Patek Philippe Wristwatches, by Martin Huber & Alan Banbery, 1998 Edition, pp. 240 to 247.