The concentration @O04358@ of an @E01960@ at a given @E01952@ (\(\text{c.d.}\)) is basically the difference in equilibrium potentials across the @D01725@. More precisely, it is the potential of a @R05229@ (of the same @E01960@ as the @W06686@ ) with the interfacial concentrations which establish themselves at \(\text{c.d.}\), relative to the potential of a similar @R05229@ with the concentrations of the bulk solution. From such a measured potential difference, with \(\text{c.d.}\) flowing, one needs to subtract the ohmic potential drop prevailing between the two electrodes.