Measurement of Electrode Potentials:

Unfortunately, there is no way of measuring directly the potential difference between an electrode and a solution. Therefore, it could be measured, with respect to an arbitrarily defined reference electrode. Like a reference electrode was first proposed through Nernst, known as standard hydrogen electrode (SHE) and was given arbitrarily zero potential (at all temperatures). Through universal agreement among chemists the standard hydrogen electrode was selected as the reference electrode.

Therefore, the electrode, whose potential is to be measured, is coupled along with a standard hydrogen electrode and the electromotive force (emf) of the resulting cell is the electrode potential of the electrode being studied, an experimental conditions being such that the liquid-junction potential is negligible.