The incoming current has to be balanced by an outgoing current of equal magnitude, so that the voltage probe draws no net current. (In Eq. (4.4) we have applied Eq. (3.14) to identify the total transmission probability N −R of outgoing edge channels with the sum of transmission probabilities Tn of incoming edge channels.) The requirement Iin = Iout determines δμ and hence the Hall resistance RH = δμ/eI: