Only 300 of these important platinum perpetual calendars were produced by Patek Philippe. The crowning achievement of the secretive "Advanced Research" division, the 5550P combined all the innovations of the 3 previous annual calendar models and was sold out before its launch! The use of Silicon in the Pulsomax escape wheel and pallet fork, Spiromax hairspring and GyromaxSi balance wheel made for the most technically advanced Patek to date. The 5550P rarely appears at auction, but when they do they are hotly contested. Complete with its special PP winding box, certificate (with blue script!), booklets caseback and stylus this one (in virtually unworn condition) is even presented with the original Patek Press Pack that accompanied the lauch in 2011.