Since the Swatch group ended the supply chain for other manufacturers Patek was forced to develop an inhouse chrono movement. And with what result! Another technical titbit is this:
inside the red lines you can see a spring (!) that is used to move the counting minute wheel. In other constructions, like Lange's Datograph, it is a system of levers that consume a lot energy. Patek has reduced the parts for this technical feature significantly by using this, again simple, spring solution.
Best
Moritz