Yes, the effect can be estimated quite easily. Also, keep in mind that the 0.13 nV is the RMS noise, so the peak to peak excursions can be around six times that, or almost 1 nV p-p. If the FS is 1 mA, then it's about 1 ppm - one count on a six digit DVM, or ten times more with each additional digit. In reality, one ohm would be commensurate with a higher range like hundreds of mA, so the noise voltage would be much further down as a percentage of FS. Also, it's hard to amplify up from a very small FS value up to the native range of high resolution DVMs without adding even more noise and thermal effects, so it makes sense to use more resistance - and undesirable burden - to get a decent FS signal that needs less amplification, but the resistor noise would be higher. It's part of the tradeoffs needed in design. When comparing current range performance to that of the voltage ranges, you should compare to the voltage range that is closest to the FS burden in order to take into account the noise and error contribution of the required amplification. Also, the specs should include the effect of amplifier bias current, which introduces additional error on high sensitivity (low I-FS) ranges. In the pursuit of ever-higher DC resolution, once you get down to where individual to tens of nV are significant to your signal, realistic resistance values contribute significant noise. If your signals are big, then it's insignificant. That's one of the reasons why the native range of the DVM is made as big as possible. Ed