Vo= Voltage parameter of adoptor:Io = Current parameter of adopter

Therefore Ro = Resistance of adopter(imaginary?) = Vo/Io

Add a resistance R1 to the connecting wire of adopter to instrument

Inew = Current value after the resister = Vo/(Ro + R1)

Therefore the voltage across the resistor =(R1/Ro+R1) Vo

Does the above make sense?