The experimentally obtained controller gain which gives stable and consistent oscillations for closed loop systems, or the ultimate gain, is defined as Ku . Kc is the controller gain which has been corrected by the Ziegler-Nichols or Cohen-Coon methods, and can be input into the above equation. Ku is found experimentally by starting from a small value of Kc and adjusting upwards until consistent oscillations are obtained, as shown below. If the gain is too low, the output signal will be damped and attain equilibrium eventually after the disturbance occurs as shown below.