Three advantages accrue from the use of operational amplifiers (OAs) in controlled-potential instrumentation, as described in Chapter 6. These are: (1) many independent input signals can be accurately summed and applied to the cell; (2) potential control is relative to a reference electrode which is subject to negligible current; and (3) accuracy of potential control is essentially independent of the reactions at the auxiliary electrode and also of the solution resistance between the auxiliary and reference electrodes. The improvements over the traditional scheme (low-impedance voltage divider and two-electrode cell) are especially significant with measurement techniques involving moderate to high frequencies or step changes in potential.