A method for the auto-calibration of PI and PID controllers, using a frequency domain model of the plant to be controlled (obtained by relay excitation), is presented. The tuning rules are inspired from the symmetrical optimum principles, introduced by Kessler [Regelungstetechnik, 6, 395-400 and 432-436 (1958)]. They have the advantage to take into account both robustness aspects (phase margin, gain margin, sensitivity, neglected dynamics) and desired closed-loop characteristics, and to cover a large domain df current, real applications. The proposed method is compared with the Ziegler-Nichols method (theoretically and experimentally). Simulations and results from industrial experiments are given.