Consequently, the stability of the open-loop transfer function must be known. Additionally, if the contour passes through the critical point (−1, 0), the system is marginally stable. The system sensitivity to disturbances can be assessed through maximum peak criterion (MPC), which interprets the system sensitivity from the minimum distance of the Nyquist contour to the critical point. The distance to the critical point corresponds to the disturbance attenuation at that frequency. The sensitivity function for the impedance-based analysis can be derived straightforwardly from