(1) the indication ‘H’ or ‘F’ to identify if the rotor is balanced with half – or full key in the keyway.(2) the identification ‘U’ for over critical rotor bearing design(3) the rotor mass in case it exceeds 1 ton.Rotors of 2-pole machines shall be balanced to minimum grade G 2.5, 4-pole and higher shall be balanced to minimum grade G 6.3 as specified in ISO 1940.