# Ziegler-Nichols tuning rules don't quite match the original gains from the Ziegler-Nichols paper

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 Edition Second 3.0j 31 Aug 2019 Richard Murray murray@cds.caltech.edu 11 12 8 Closed

The gains listed for the original Ziegler-Nichols tuning rules don't quite match what was in the original paper:

• For the step response method, the integral time constant for a PI controller should be T_i = \tau/0.3 (instead of 3 \tau).
• For the frequency response method, the proportional gain for a PI controller should be k_p = 0.45 k_c (instead of 0.4 k_c and the integral time constant should be T_i = T_c/1.2 (instead of 0.8 T_c).