Consider a plant with the transfer function G(s) = 1/(s + 1)3. Let Ku and Tu be the ultimate gain and ultimate period corresponding to the frequency response based closed loop Ziegler-Nichols cycling method, respectively. The Ziegler-Nichols tuning rule for a P-controller is given as : K = 0.5 Ku. The gain of the transfer function between the plant output and an additive load disturbance input of frequency 2Ï€/Tu in closed loop with a P-controller designed according to the Ziegler-Nichols tuning rule as given above is