It is not possible to measure the electrode potential Eoref for a single reaction in isolation. Rather, two reactions must occur simultaneously in order the compare the potential difference between them.
All reactions are paired with the reaction for dissolved hydrogen ions. Both the test reaction and the reference reaction are maintained at 1 molar concentrations (i.e. 1 gram-mole per liter), in an environment of 25 °C and 1 atm pressure.
For concentrations and temperatures other than 1 molar and 25 °C, the electrode potential Eo can be recalculated using the ,
where k is Boltzmans constant (8.61 × 10-5 eV/K), n is the number of electrons exchanged in the reaction, T is the temperature (in Kelvin), C is the molar concentration.