In order to know the exact polarization level in a buried metallic structure or the bottom plates of an above ground storage tank we need to know how to locate the polarized potential on polarization curves. It means that a polarized potential is an IR drop free potential which indicates the real level of polarization. One of the common methods to find out this polarized potential is referred to as instant-off potential measurement. In this method the potential of the structure needs to be read immediately after rectifier interruption. It is not an easy job to locate the exact point of instant off potential. What do you think about the attached depolarization curve ? Which point indicates the exact polarized potential ?