FIGURE 17.

The unbiased counting frame. A section containing 14 objects (a) is successively divided first parallel to the y‐axis (b) and then parallel to the x‐axis (c). Along the dividing lines, the same counting rules that have been established along the z‐axis are now applied along the x‐ (b) and then x‐ and y‐axes (d). Fifteen objects instead of 14 are detected if all objects fully contained within the squares and all object fragments touching a green inclusion line are counted in (c). The overcount is due to the double count of the cell labeled with the question mark. The double count is avoided by the extension of the red exclusion lines in (d) [Color figure can be viewed at wileyonlinelibrary.com]