One of the most important problems in the area of process control is the assessment of dynamic performance. Traditional measures such as overshoot, rise time, decay ratio, settling time, and the ISE are difficult to translate into an economic measure for justification of process or control system redesign. Research has shown that frequency domain measures (the maximum closed-loop regulator log modulus) can be used to provide a measure of performance that can be translated into an economic measure. Unfortunately, this assessment requires the existence of an accurate linear model of the process. For processes that are highly nonlinear and complex, these models are difficult to obtain. A new test, the LATV test (load autotune variation test), is presented that locates the peak regulator log modulus experimentally. The LATV test is a closed-loop test that involves the insertion of a relay from a controlled variable to a given load disturbance with the feedback controller on automatic. This causes the plant to exhibit a sustained oscillation at the frequency where the regulator log modulus curve exhibits a peak.