The HUD shows 0% or 100% when key pressed to cycle or advance the superchargers. It has no effect. I flew a Ju 88 with one engine set at 0% and the other at 100% and they tracked identically and both switched to 2nd gear at ~3400m. Ju 88 and many other aircraft had two speed superchargers that could be either run on automatic gear changing or selected to run on either of the gears and shifted manually using the lever. Key mapper should allow for setting the supercharger to Auto--->1st Speed---> 2nd Speed
thanks

skud