The relationship between the maximum and random reflectance of vitrinite, R-max and R-r, for Upper Silesian coal is represented by the equation: R-max = 1.090R(r) - 0.052. When the random reflectance is higher than 0.90%, the difference between R-max and R-r values becomes significant. R-max is a more precise rank indicator, the standard deviation is much smaller than the standard deviation of the random reflectance value, which is larger due to the optical anisotropy of vitrinite.