Instant off is the process of taking measurements the instant you turn off power to an impressed current CP system. When you have multiple current sources, you must turn them off simultaneously using synchronized interrupters. The purpose of turning all the current sources off is to eliminate the IR drops in the circuit. As current (I) flows through cabling there is a resistance (R) that the current must overcome – this is known as voltage drop because V=I x R. When attempting to measure the level of polarization, it is important to eliminate the IR drops in the circuit that are the result of current flow creating these IR drops. By instantaneously turning the current off, the IR drop readings immediately reduce to zero because the current (I) is now zero. This means that the polarization you measure immediately after turning off the current is the true polarization current. Timing is critical because with the current turned off the structure will immediately depolarize. The polarization potential will begin to decay. The goal of instant off polarization readings is to catch the polarization level as you turn power off and before the depolarization process begins.