An analysis used in process control to determine the output signal as the result of a disturbance in a system. It involves both the magnitude and phase angle of the output signal as a function of frequency in comparison with the input signal. The magnitude is typically measured in decibels and the phase angle is measured in radians. The frequency response of a system can be analysed by plotting the magnitude and phase on a chart. The three commonly used frequency response diagrams are the Bode plot, the Nyquist plot, and the Nichols plot.