I've been told that something like a worn advance piston can be repaired without having to go through a calibration, but for what it costs I like the peace of mind. My rebuilder gave me a more intelligent description of what your seeing in the pics, and what he said is each fuel line goes into what is basically a precision injector and then the calibrating fluid travels into a graduated cylinder moving a puck style piston downward for volume measuring purposes. The internal pressures are monitored via separate gauges. The black bracket attached to the side window of the pump actually has a timing pin that is measuring cam travel (i.e. advance movement). He can then measure pump output for any given speed as well as set up the idle speed and max RPM, control the torque rise, set up the automatic advance curve and light load advance and more.