= can also be found on the Nyquist plot as the

The denominator, where IG(s)l-1 = 0, can also be found on the Nyquist plot as the distance from the point (0, -1) to the point on the plot. Now we know both the numerator and denominator on the Nyquist plot and if we calculate various values around the plot, we can construct our closed loop frequency response. In the same way our closed loop phase angle can be found as

<PeL = <PoL - ~ Instead of having to perform these calculations for each point, it is common to use a Nichols chart where circles of constant magnitude and phase angle are plotted on the graph paper. After we plot our open loop plot (as done for a Nyquist plot), we mark each point were our plot crosses the constant magnitude and phase lines for the closed loop. All that remains is to simply record each intersecting point and construct the closed loop response.