A while back, Mr PPCB posted that the unit he traced was calibrated to:
Q1 - 4.45v
Q2 - 4.3v
Q3 - 4.46v
Q4 - 4.75v
And to add to the previous advice, i usually just stick the ground probe into one of the screw holes on the chassis. Assuming everything is grounded properly, I find this to be...