Combination of the Bürker and Thoma system. The chamber depth is 0.1 mm. The ruling shows 9 large squares of 1 mm2 each. The large squares are subdivided into 16 group squares with 0.2 mm side length. In the central large square, each group square is subdivided into 16 mini squares with 0.05 mm side length (= 0.0025 mm2).