In the upcoming engine overhaul, a nut is welded in by the workshop, so that afterward the ignition/gasifier (SU-H2) can be adjusted correctly by the test device. My idea is to install a permanent probe later and determine the ratio via the voltage that the probe provides. As I understand it, the probe needs a preheater (12V positive earth available) and probably deliver a linear flattening of 0 to 1V. If this is confirmed here. the value would have to be verifiable with a simple measuring instrument.