Abstract: A method of balancing a set of retaining and locking plates used to retain a row of gas turbine engine aerofoil blades in attachment to a rotor disc, includes: (i) providing a weighing plate having a circular track; (ii) providing a non-rotating, static balancing apparatus capable of detecting unbalance in the weighing plate; (iii) positioning the weighing plate on the static balancing apparatus, and positioning the set of retaining and locking plates on the track in an arrangement corresponding to a possible arrangement for the set of plates in use in the engine; and (iv) repositioning the retaining and locking plates on the track to arrive at a balanced arrangement for the set of plates.