zones 14 containing marking substance are shown fig2 depicts a round strainer 2 of a paper making machine in schematic side and top elevational views with a pulp input 4 partial test zones 14 discharge tube 17 control unit 18 for the discharge tubes 17 the automatic valve 19 in every discharge tube 17 the pump 20 for the circulation of the marking substance and the supply container 26 for the marking substance for the partial integration thereof fig7 depicts the signal graph as a diagram of voltage u as a function of the number of channels during scanning of the optical scanner sensors 10 and of the capacitive scanning sensors 11 over a bank note with homogeneously distributed marking substance and with an electrically conductive embossed section the sensor channels 1 14 are depicted schematically fig7 a depicts the combining of the signals of the optical scanning sensors 10 of the capacitive scanning sensors 11 and of the optical sensors 13 which actuate the capacitive scanning sensors 11 during testing of a web provided with partial test zones 14 fig8 is a schematic side elevational view of a water mark embossing roller 5 with embossing segments 25 and with a marking substance transfer roller 7 an electrically conductive test zone 9 structured as a water mark 9 a supply container.