The relationship that describes the electrode potential as a function of the current of a reversible redox system (reversible electrode reaction) in the steady state in voltammetry \[E = E^{\circ\prime} - \frac{RT}{zF} \ln \left(\frac{D_{\rm{red}}}{D_{\rm{ox}}}\right)^s \pm \frac{RT}{zF} \ln \left(\frac{I_{\rm{d,lim}} - I}{I}\right)\] where \(E^{\circ\prime}\) is the formal electrode potential, \(z\) the electron number of an electrochemical reaction, \(D_{\rm{red}}\) and \(D_{\rm{ox}}\) the diffusion coefficients of the reduced and oxidized forms of the electroactive substance, respectively, \(I_{\rm{d,lim}}\) is the limiting diffusion current, and \(I\) is the current at the potential being applied. The value of the exponent \(s\) is ½ for a stationary or dropping mercury electrode, ⅔ for a hydrodynamic electrode (see hydrodynamic voltammetry), or 1 for a microelectrode. In the equation, the last term is added for reduction and subtracted for oxidation.