The use of screened fractions at the simplest level is done to provide cleaner data by helping to reduce touching particles and the bias that can be introduced through stereological effects. There are well documented reasons based on the mathematics of converting 2d section images into 3d particles (stereology), which show that if we want to generate a meaningful grain size distribution it should be required that screened fractions are analysed. Stereological corrections work well because they calculate 3d parameters based on a statistically random distribution of particle orientations.