When two metals are electrically isolated from each other, an arbitrary voltage difference may exist between them.
Rather, this small increase or decrease in charge results in a shift in all the energy levels in the metals.
The Galvani potential difference between an electrode and electrolyte (or between other two electrically conductive phases) forms in an analogous fashion, although the chemical potentials in the equation above may need to include all species involved in the electrochemical reaction at the interface.
The Galvani potential difference is not directly measurable using voltmeters.
It is noted that[4][5] what one experimentally measures using an inert metallic probe and a voltmeter is