The complex angle θ θ = arg ⁡ ⁡ ( Z ) = − − arg ⁡ ⁡ ( Y ) is the phase difference between the voltage and current passing through a component with impedance Z. For capacitors and inductors, this angle is exactly -90° or +90°, respectively, and X and B are nonzero. Ideal resistors have an angle of 0°, since X is zero (and hence B also), and Z and Y reduce to R and G respectively. In general, AC systems are designed to keep the phase angle close to 0° as much as possible, since it reduces the reactive power, which does no useful work at a load. In a simple case with an inductive load (causing the phase to increase), a capacitor may be added for compensation at one frequency, since the capacitor's phase shift is negative, bringing the total impedance phase closer to 0° again.