Inclusion Class 1. Defines the sum of the cross section in mm2 of inclusions per 100 cm3 of glass. Inclusions with a' diameter < 0.10 mm are disregarded. 2. Refers to the diameter of the largest single inclusion. 3. Index homogeneity: the maximum index variation (relative), measured over the clear aperture of the blank. 4. Index homogeneity is certified using an interferometer at 632.8 nm. The numerical homogeneity is reported as the average through the piece thickness. Blanks with a diameter up to 450 mm can be analyzed over the full aperture. Larger parts can be analyzed using multiple overlapping apertures. The minimum thickness for index homogeneity verification is 20 mm. For thinner parts, the parent piece is certified.