A Nichols plot is useful for quickly estimating the closedloop response of system with unityfeedback, given its openloop transfer function. For example, let the openloop transfer function be:
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By default a Nichols plot includes constantphase and constantmagnitude contour plots of a closedloop system. From the graph below, the peak closedloop response is about 5 dB, at 0.8 rad/s, because that is the highest constantmagnitude contour that it touches (estimating).
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