Comparison of the results the non-contacting and contacting measurements of the electrostatic potentials on the surface of the dielectric plane indicates that knowledge of the spatial resolution of the instruments used in experiment is very important. Very frequently the surface charge distribution is nonuniform, and investigation of such nonuniformity can become quite challenging. A contacting ESVM proves to be very useful in this case, providing potential readings from the very well defined area of contact. By using the Comsol modeling, authors tried to prove that direct comparison of the mathematical models (finite element analysis, in this case) with measurement results obtained via non-contacting methods requires good knowledge of measurement principles (spatial resolution).