In the same way that BV kinetics can be linearized at small overpotentials (i.e., about a current of zero), the kinetics can also be linearized about any value of applied current, even within the non-linear region of the kinetics. The slope of the overpotential versus current curve has units of resistance (𝑅 = 𝑉/𝐼). The charge-transfer resistance (Rct) can be visualized as the average slope of the overpotential versus current curve between the origin and the applied current (Fig. ). By extension, the differential charge-transfer resistance can be visualized as the local slope (𝑑𝑉/𝑑𝐼) of the overpotential versus current curve at any point (I, η) on the curve. Similarly, the linearized charge-transfer resistance (𝑅 𝑐𝑡 0 ) can be visualized as the local slope of the overpotential versus current curve at a current of zero. The differential charge-transfer resistance (𝑅 𝑐𝑡 ′ ) can be formally defined as the rate of change of overpotential with respect to current: