The value of the potential of a given electrode with respect to a suitable reference electrode when appreciable contributions to the total anodic and/or cathodic partial currents are made by species belonging to two or more different couples, but the total current is zero, i.e. \[I=\sum _{\begin{array}{c} i \end{array}}I_{i}=0\qquad (I_{i}\neq 0)\] where Ii is the partial current of reaction i \[I_{i}=I_{i,a}+I_{i,c}\]