C3H5N3O9 Experiment ZR012 ~ brainchild of Max Büsser (MB) and Felix Baumgartner (URWERK), it is the first watch to use an eccentric planetary transmission system for the timekeeping mechanism - i.e. the same geometry as the Wankel engine.
Overall, the 5204 is an astounding new addition to the Patek Philippe lineup. It maintains the iconic Patek perpetual calendar split-second chronograph DNA while using cutting-edge watchmaking techniques to make the new iteration even more technically impressive than the last. For a highly complicated watch in a 40mm case, the dial is clean, easy to read, and just flat out beautiful.