A new phase-shifting interferometric technique vising an arbitrary phase step is described in which the step is determined using an algorithm called probabilistic global search Lausanne. The algorithm characterizes the piezo-actuator nonlinearity and precisely estimates the vibration induced during piezoelectric transducer translation. The unknown linearly varying phase step is calculated with around 0.082% error. A least-squares fit is subsequently applied for the measurement of interference phase once the exact phase step is known. © 2005 Taylor & Francis Ltd.