Cancels and replaces the second edition (1977). Specifies the equipment for measuring the diffuse reflectance factor of pulp, paper and board and the procedures for calibrating that equipment. Measurements are used for the evaluation of optical properties such as diffuse blue reflectance factor, the scattering coefficient of pulp, opacity, whiteness, luminous reflectance factor, the chromaticity coordinates of paper and the intrinsic reflectance factor of non-fibrous materials. Numerical values optically characterizing the materials are calculated specifically for each property determined.