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The first Patek Philippe watch with a SpiromaxR spring: the Ref. 5350 Annual Calendar in a limited "Patek Philippe Advanced Research" special edition A pioneering invention like the SpiromaxR spring deserves to be showcased. A second limited "Patek Philippe Advanced Research" edition of the self- winding Annual Calendar Ref. 5350 in 18K rose gold is therefore being launched on the occasion of Baselworld 2006. Its caliber 324 S IRM QA LU is the first movement fitted with a SpiromaxR spring made of SilinvarT. As a further exclusive feature, it is also equipped with a silicon escape wheel. To do justice to these technical innovations, the movement has a specially shaped balance cock that reveals a large portion of the SpiromaxR spring and the going-train bridge is milled so that the mysterious blue-violet sheen of the nearly black silicon escape wheel is more readily visible. Additionally, the sapphire-crystal back has an integrated loupe and bears the inscription "Patek Philippe Advanced Research." The solid 21K gold winding rotor features a zirconium ball bearing. Like the silicon escape wheel, the balls run dry and never need to be lubricated. The edition of this "Patek Philippe Advanced Research" model, the Ref. 5350R, is limited to three hundred watches.