This part of ISO 1940 gives specifications for rotors in a constant (rigid) state. It specifies a) balance tolerances, b) the necessary number of correction planes, and c) methods for verifying the residual unbalance. Recommendations are also given concerning the balance quality requirements for rotors in a constant (rigid) state, according to their machinery type and maximum service speed. These recommendations are based on worldwide experience. This part of ISO 1940 is also intended to facilitate the relationship between the manufacturer and user of rotating machines, by stating acceptance criteria for the verification of residual unbalances. Detailed consideration of errors associated with balancing and verification of residual unbalance are given in ISO 1940-2. This part of ISO 1940 does not cover rotors in a flexible state. The balance quality requirements for rotors in a flexible state are covered by ISO 11342.