 The activity of ions at the electrode surface changes when there is current flow, and there are additional overpotential and resistive loss terms which contribute to the measured potential.At very low concentrations of the potential-determining ions, the potential predicted by Nernst equation approaches toward .This is physically meaningless because, under such conditions, the exchange current density becomes very low, and there is no thermodynamic equilibrium necessary for Nernst equation to hold.The electrode is called unpoised in such case.