ISO 21940-11:2016 establishes procedures and unbalance tolerances for balancing rotors with rigid behaviour. It specifies a) the magnitude of the permissible residual unbalance, b) the necessary number of correction planes, c) the allocation of the permissible residual unbalance to the tolerance planes, and d) how to account for errors in the balancing process. NOTE In ISO 21940‑14, the assessment of balancing errors is considered in detail. Fundamentals of rotor balancing are contained in ISO 19499 which gives an introduction to balancing. ISO 21940-11:2016 does not cover the balancing of rotors with flexible behaviour. Procedures and tolerances for rotors with flexible behaviour are dealt with in ISO 21940‑12.