I use my K181 in talk-only-mode, since i also couldnt get it to answer on requests in GPIB.

@HighVoltage: Indeed, Johnson-noise limits the measurements. See for example:

http://www.emelectronics.co.uk/a20.html -> "

Noise.

Equivalent noise resistance less than 10 ohms. Noise voltage depends on bandwidth e.g. rise time constant 10 seconds gives peak to peak noise voltage of 250 picovolts."

"With source resistances below 10 ohms, the noise is substantially

constant down to zero ohms. Above 100 Kohms, the noise voltage

increases over the thermal noise characteristic by about 10 dB per

decade of source resistance."