I just remembered an incident where over TOL's airspace I was transversing VFR, but there was an IFR cessna that was having an apparent Transponder issue. Was supposed to be at 5000, but was registering 5500. Toledo was getting frustrated, and kept repeating back the Baro @ 30.40, etc.. Finally come to find out the dumb was setting his altimeter to the pressure altitude displayed on his magic transponder. Nice work! I wish I could remember the details of the converstation, but it was basically the Skyhawk guy was 100% confident he was right.