the greatest watch models in the world. Historically, only 349 pieces of Ref. 2499 were made from 1950 to 1985 - around 9 pieces each year. Over the course of 35 years, four series of Ref. 2499 were introduced, exerting a strong influence on the watch designs of many other renowned watchmakers. As of June 2019, Ref. 2499 holds eleven spots among the 59 world's most expensive watches sold at auction (over 2 million US dollars) and at least 18 pieces of Ref. 2499 have been auctioned for more than 1.5 million US dollars, with the world record being 3.880 million US dollars (3,915,000 CHF) made at Sotheby's Geneva auction on November 13, 2018. The successors to Ref. 2499 include, in chronological order, Ref. 3970, Ref. 5970 and Ref. 5270. Sky Moon Tourbillon Patek Philippe Sky Moon Tourbillon wristwatch was introduced in 2001, with Ref. 5002 being the first model. The wristwatch has two dials and contains 12 complications including tourbillon, minute repeater, sky chart, and moon phase & orbit. In 2013, the company introduced the second model of Sky Moon Tourbillon, Ref. 6002, also with 12 complications. The new model took 7 years of research and development, while the engraving on each piece alone took more than 100 hours. Sky Moon Tourbillon was the most complicated wristwatch from Patek Philippe until 2014. It is estimated that only 3 - 5 pieces are made each year, and the price for each piece is over US$1.2 million. However, every purchase of the piece requires an application from the buyer and has to be approved by Patek Philippe President Thierry Stern. On October 2, 2018, a Sky Moon Tourbillon 6002G was auctioned by Poly Auction in Hong Kong, fetching US$2.707 million (HKD 21,240,000), making it one of the most expensive watches ever sold in auction. 150th anniversary edition In 1989, Patek Philippe created Calibre 89, then the most complicated mechanical watch ever made, for its 150th anniversary. Calibre 89 holds 33 complications, including the date of Easter, time of sunrise, equation of time, sidereal time, and many other indicators. 1,728 unique parts allow sidereal time, a 2,800 star chart, and more. In addition, Calibre 89 is able to add a day to February for leap years while leaving out the extra day for every 100 year interval. Only four pieces of Calibre 89 were ever manufactured by Patek Philippe, with one in