Putting the differential amplifier into the circuit being measured, one can see how all of the problems with the single ended scope measurement are eliminated. Notice that both input leads present the same high impedance load to the circuit under test, referred to as being balanced. A good test to see if an unbalanced technique is affecting the measurement is to reverse the input leads. (Do not do this with a floating scope on circuits sensitive to excess loading capacitance.) Ideally, the waveform should be a identical but inverted. If any change in the waveform is noticeable when the input leads are reversed (use the invert function of the scope if necessary), then the circuit is susceptible to the effects of unbalanced loading.