Typically we use permanent only to monitor problem areas (such as suspected interference locations) or perhaps a critical location, generally where we need to take readings more often. So you could install a permanent electrode and take readings and have someone monitor it at a specified fequency, even hook up a datalogger, the CP vendor can use this data in analysis, or have compamnies own people monitor rather than calling the CP vendor every time. As far as the readings between permanent and portable, they are the same (assuming electrode type is the same).