Limits of a comparative evaluation of the performance of a conventional X-band marine radar (MR) sigma S6 WaMoS® II used for surface current measurements are dicussed. Main focus of the paper is to address challenges when comparing current measurements from different measuring devices for evaluation purpose. Although the current measurement principles of MRs and acoustic Doppler current profilers (ADCPs) are disparate, they are often used to validate the quality of MR current measurements. In fact, differences in MR and ADCP derived currents can have a variety of physical reasons and do not necessarily indicate measurement errors. One possible cause of deviation is the comparison of dissimilar quantities.