Harmonic response analysis computes the steady-state dynamic response of a system to sinusoidal loads. The most efficient way to capture the harmonic response is the mode superposition method, which linearly combines different mode shapes to obtain the deformation response. In order to achieve complex deformation shapes, a higher number of mode shapes may be required. This increases the computational cost correspondingly. Residual vectors can be used to improve solution accuracy with fewer mode shapes in certain situations. They can be thought of as pseudo-modes that help to represent complex deformation shapes, thereby reducing the number of modes required for the mode superposition calculations. In this lesson, we demonstrate how and when to use residual vectors to obtain accurate results in a computationally efficient manner using Ansys Mechanical.