Abstract. This work studies the influence of the signal processing method on the flicker measurement of grid connected wind turbine in continuous operation according to the procedure detailed in the IEC 61400-21 standard. Two different methods for solving the fictitious grid are analyzed: Zero Crossing Detection and Short Time Fourier Transform. The deviations in the flicker measurement results obtained by applying both methods to actual signals from a measurement campaign are discussed. And the results are compared taking into account the grid impedance angle and the wind condition.