The controller parameters are typically matched to the process characteristics and since the process may change, it is important that the controller parameters are chosen in such a way that the closed loop system is not sensitive to variations in process dynamics. One way to characterize sensitivity isthrough the nominal sensitivity peak M_s:[1]

M_s = \max_{0 \leq \omega < \infty} \left| S(j \omega) \right| = \max_{0 \leq \omega < \infty} \left| \frac{1}{1 + G(j \omega)C(j \omega)} \right|

where G(s) and C(s) denote the plant and controller's transfer function in a basic closed loop controlSystem, using unity negative feedback.