# Original Ziegler-Nichols gains listed after improved tuning rules are incorrect

• For the step response method in equation (11.10a) the original Ziegler-Nichols gains should be $k_p = 0.9T/(K \tau)$ and $k_i = 0.27 T / (K \tau^2)$.
• For the frequency response method in equation (11.10b) the original Ziegler-Nichols gains should be $k_p = 0.45 k_c$ and $k_i = 0.54 k_c/T_c$.