Dwayne, I missed the fact that you do tie B and C together, disregard this in my previous post. Can you supply a helpfull pointer wrt. theory ? Is this based on the fact that both probe currents are several orders of magnitude above the saturation current of the junction(s) ? tia, Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics