Oh i see (and no need to get on your high and mighty) the problem then is that you have an ambiguos reading. The idea is that mV = nA, uA and mA, if you do each decade it will be so confusing it will make life harder. A multimeter reads in mV or V, to have 100mV per 1nA, 10nA, 100nA, 1uA, 10uA, 100uA, 1mA, 10mA, 100mA will be very confusing if your trying to use all ranges. Of course a more complex product could do as you want but it would be more expensive as it would need it's own display and a more complicated case.
Live and let live then
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I thought I was being fairly clear, the mV I was talking about in all cases was the voltage drop across the shunt resistor for a given current, sorry if it was confusing.
Sure, I appreciate that one of the aims of the uCurrent was to be as cheap possible to manufacture by putting everything on the PCB, unfortunately that inevitably leads to compromises like multi-way switch availability, which limits number of shunts, which.... It's what you need to do to meet the selling price and of course a weak point in comparison with what can be made one-off - as always with commercial products.
Yes, you can certainly use external shunts across the terminals, and probably a good idea to do it on the 'bottom ends' of the uA and mA ranges to trade a slightly higher voltage burden for less noise. Unfortunately not possible on the nA range as the 10k is already there - maybe an option to switch out all internal shunts would be useful addition, leaving the actual uCurrent as a low offset, high impedance amplifier (there's always an option for the user to remove the 10k of course).