The paper by Åström and Hägglund presents a method for automatically tuning PID regulators based on phase and amplitude margin specifications. The key idea is to estimate the critical gain and frequency using a simple identification method, which is robust to modeling errors and disturbances. The method involves a relay control experiment to determine the critical gain and period, and then applies classical Ziegler-Nichols tuning rules or other design schemes based on the estimated critical point on the Nyquist curve. The paper discusses the theoretical analysis of the method, including conditions for limit cycle oscillations and stability. Practical aspects such as measurement noise, level adjustment, and actuator saturation are addressed. Experiments on laboratory and industrial processes demonstrate the effectiveness of the method, showing that it is robust and easy to implement. The paper also explores the use of the auto-tuner for initializing adaptive controllers, highlighting its potential for tuning a wide range of control problems.The paper by Åström and Hägglund presents a method for automatically tuning PID regulators based on phase and amplitude margin specifications. The key idea is to estimate the critical gain and frequency using a simple identification method, which is robust to modeling errors and disturbances. The method involves a relay control experiment to determine the critical gain and period, and then applies classical Ziegler-Nichols tuning rules or other design schemes based on the estimated critical point on the Nyquist curve. The paper discusses the theoretical analysis of the method, including conditions for limit cycle oscillations and stability. Practical aspects such as measurement noise, level adjustment, and actuator saturation are addressed. Experiments on laboratory and industrial processes demonstrate the effectiveness of the method, showing that it is robust and easy to implement. The paper also explores the use of the auto-tuner for initializing adaptive controllers, highlighting its potential for tuning a wide range of control problems.