An emf produced at the surface of electrodes. Usually considered a result of corrosion. Electropolarization potential generally is large when an electrode is first placed into a medium (ground or drilling mud), and decreases with the passage of time. Electropolarization on a remote [[SP]] electrode produces spurious displacement on the SP curve which is balanced electrically by a compensation voltage applied by a [[millivolt box]]. Since the applied voltage is constant and the electropolarization potential changes with time, a drift on the SP curve can result.