Consider a first-order plus delay model defined by the transfer function , where , , and are the gain, time constant, and time delay, respectively. In order to find and , Sundaresan and Krishnaswamy [1, 2] use the normalized response of the model to a step-forcing function: at two different times, and . These times are selected such that the normalized response reaches 35.3% at and 85.3% at . The recipe gives the estimated values of the time constant and delay time by and .