The invention relates to a microelectronic device with means for the determination of the wetting grade of a sensitive surface that lies adjacent to a sample chamber with a sample fluid. The residue of stencil material M in a stencil material roll is calculated by residue calculating means and the elapsed time of the stencil material roll from production thereof is obtained on the basis of date data on the date of production of the stencil roll. At least one analysis values representative of the video sequence is formed by forming the average of the corresponding analysis values of the frames of the video sequence. The first roller pair forms a thermal conditioning pre-seal between opposing surfaces of the overlapping layers by application of heat and pressure along the peripheral surfaces of the first roller pair.