I tested a little the ohm function of the 34401A for the sake of implementing the Bruce's idea of using the internal current source as reference. The instrument offers substantially two useful ranges with 1mA test current: 100 ohm and 1K ohm. In the 100 ohm range, the voltmeter measure 0-100mV plus 20% overrange as usual; in the 1K ohm, measure 0-1V. All other ranges have different test currents and the voltmeter always measure 0-1V or higher. Wonder why they didn't add a way to measure 1K with 100uA and 10K with 10uA: it would have made the instrument much more useful in the case of self heating of DUT. Tomorrow I'll try the stability of the current source against the reference of another 34401A. Best regards, Andrea Baldoni