At the dielectric measuring the material situated in the measuring area is penetrated of an electric magnetic field whose properties are determined fundamentally by the available material moisture. Because of the distinctive polarity of the water molecule and the high dielectric constant of water of about 83 in comparison approximately to paper (natural fibres have a dielectric constant of 2) the capacity of a measuring area is dominantly determined by the quantity of free water molecules into paper. Based on a constant volume the moisture value at hand-held test equipments is calculated from the measuring signal. The measuring area up to a depth of 300 mm should as completely as possible be filled out with the waste paper.

Contaminations, how conductive foils, metals etc. lead to extremely divergent measurements or to switch off of the equipment.