The ability to measure this current flowing in both directions is enabled by applying a voltage to the REF terminal, as shown in Figure 8-5. The voltage applied to REF (V_REF) sets the output state that corresponds to the zero-input level state. The output then responds by increasing above V_REF for positive differential signals (relative to the IN– terminal) and responds by decreasing below V_REF for negative differential signals. This reference voltage applied to the REF terminal can be set anywhere between 0 V to V_S. For bidirectional applications, V_REF is typically set at mid-scale for equal range in both directions. In some cases, however, V_REF is set at a voltage other than half-scale when the bidirectional current is non-symmetrical.