I have 34450A and use it for 4-Wire measurement. Multimeter use for measurement 1mA current. I have connected both Hi Sense and Hi Input terminals to conducor and both Lo Sense and Lo Input are not connected to any point. Then I connect only Lo Sence to same conductor as Hi sence and Hi Input and measure 0.005ohm despite current loop is not closed(Lo Input is not connected). I would expect that when no 1mA current is present no measurement takes place.