After sectioning the structure into slabs, estimate the area of the region of interest in each slab on a section from the face of the slab. This is performed before the second sectioning, which results in vertical sections. The amount of sampling in the vertical sections that stems from a particular slab should be proportional to the area of the slab, before the generation of the vertical sections, that is, the second sectioning. (Courtesy of Lutz Slomianka.)