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The second round of an interlaboratory comparison program for extremely low frequency electric and magnetic fields measurements was performed at the High Voltage Laboratory of the National Technical University of Athens (Greece). The 16 participating laboratories measured the following: (i) electric field produced by a scale transmission line; (ii) magnetic field produced by a medium voltage cable; and (iii) magnetic field and frequency at the center of a standard square coil and their delivered results were evaluated in all measurement scenarios with use of performance statistics z-scores. Deviations between z-scores based on usual estimators (mean value, standard deviation) and robust estimators (derived with the robust algorithm described by the International Organization for Standardization [ISO, 2005]) highlight improved performance of the robust algorithm. An overall comparison to measurement procedure and performance results of the first round proves effectiveness and necessity of the scheme. Improper instrumentation or calibration, instability of the field source and measurement position uncertainty are factors that may cause unsatisfactory performance of the participants.