The material moisture content of paper (and also textiles or films) on running webs may be influenced by the surrounding environmental conditions (humidity | tem- perature), alterations in the parameters of the raw materials or by other mechanical influences leading to changes and loss of quality. Determination of the equilibrium moisture content traversing the running web can allow conclusions to be drawn on the material moisture content of the paper. For the further processing of the paper the equilibrium moisture is important and is specified accordingly, however, the material moisture content of the paper is the decisive factor in production.