 This method was developed in 1953 and is based on a first-order + time delay model.Similar to the Ziegler–Nichols method, a set of tuning parameters were developed to yield a closed-loop response with a decay ratio of 1/4.Arguably the biggest problem with these parameters is that a small change in the process parameters could potentially cause a closed-loop system to become unstable

Published in 1984 by Karl Johan Åström and Tore Hägglund, the relay method temporarily operates the process using bang-bang control and measures the resultant oscillations.