8.1.1.1 Electrical measurements and inspections are necessary to determine that protection has been established according to the applicable criterion and that each part of the CP system is operating properly. Conditions that affect protection may change with time, however, and corresponding changes are required in the CP system to maintain protection. Periodic measurements and inspections shall be made to detect changes in the conditions that affect the CP system. Local conditions may exist in which operating experience indicates that surveys and inspections should be made more frequently than recommended herein.