The Patek Philippe Complications collection gathers the brand's annual calendar, chronograph, moonphase, world time, and other single and combined complication references into one of the most technically prestigious groups of wristwatches in existence. Patek Philippe has been instrumental in advancing the state of complication watchmaking throughout its history: the brand produced the first perpetual calendar wristwatch, the first minute-repeating wristwatch, and continues to develop new complications with each generation. Key pre-owned Complications references include the ref. 5396 annual calendar, the ref. 5905P annual calendar with flyback chronograph, the ref. 5327 perpetual calendar, the ref. 5370P split-seconds chronograph, and the ref. 5531 world time with enamel dial. The annual calendar complication — which Patek invented and patented — distinguishes between 30- and 31-day months automatically, requiring a single correction per year. The pre-owned Complications market attracts buyers who seek mechanical substance behind the Patek Philippe name, with prices spanning a wide range depending on the complexity involved, case material, and reference rarity. DeMesy & Co. in Dallas has been evaluating and authenticating pre-owned Patek Philippe Complications references since 1987, applying rigorous standards to each piece.