Patek Philippe has continually produced perpetual calendar link and perpetual calendar chronograph wristwatches since 1941. No other brand would produce a serially produced perpetual calendar wristwatch until 1955, when Audemars Piguet introduced the groundbreaking ref. 5516 (the first perpetual calendar wristwatch to indicate the leap year), and it wouldn't be until 1985 when another brand link would produce a perpetual calendar chronograph in link series – IWC with the Da Vinci Chronograph. link