I'v been watching my scan gauge for about 3 months now with out being able to make any sense out of it. It seems like you need to be driving on flat land at a constant speed with no wind to get a reading you could tune your vehicle to. I installed a wideband AFR meter last week and that works very good. My truck runs at 14.4:1 AFR all the time. Once the HHO offset is established I'll tune to that.