With the sidewinder 3d pro it uses an optical sensor with an ir source, then it converts those signal into x-y analog signal using a signal processor so that the old style midi game ports can get the analogue co-ordinates, since the joystick movements are processed digitally the analogue outputs are always the same (including min-max and center range co-ordinates), because of this the data for the co-ordinates range is stored in the firmware of the teensy for these joysticks. With potentiometer type joysticks calibrations would have to be carried out as the values drift due to wear and tear, humidity and other factors but these joystick don't suffer from these issues due to the detectors being contactless.