Attached is today's data. Same experiment, same location, same A/C settings, same 'weather' outside. Only difference, the stand-by generator for the house did not run. So much for reproducibility. Today's capture was 13,198 data points. Seems less 'oscillatory' and 'bunched' around -1.6 uV. Now, if I can figure out how to do the 'MODE, TEST 0' which I believe to be an RS232 command, I will re-capture tomorrow. Mickle, if I understand, place the short, do the command, then capture data. Correct? Joe