https://doi.org/10.1351/goldbook.M03944

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 \[I_{i}=I_{i,a}+I_{i,c}\]*Source: *

PAC, 1974,*37*, 499. 'Electrochemical nomenclature' on page 513 (https://doi.org/10.1351/pac197437040499)

PAC, 1974,