I was able to get the DSO Quad to reflect accurate voltages on both the A and B channels. I was getting what I would describe as some offset voltage, always more that what should have been indicated. I found that if I moved the zero voltage all the way down to the bottom of the screen (using the Y adjustment) the voltage reading were good. I do feel I can get reliable voltage readings out of this unit now. I did spend a long time calibrating and recalibrating the voltages.
Take care.
–Spiro