The purpose of material screening is to hope that all the particle sizes smaller than the screen holes in the feed to the screen enter the undersize product. However, under industrial production conditions, it is very difficult to achieve this goal, and the oversize product always contains some fine particles smaller than the screen holes. In order to evaluate the completeness of the screening process, screening efficiency for round vibrating screens is introduced. This refers to the ratio of the actual mass of material smaller than the screen holes obtained in the screening product to the mass of such material contained in the feed.