A system includes an adjustable implant configured for implantation internally within a subject and includes a permanent magnet configured for rotation about an axis of rotation, the permanent magnet operatively coupled to a drive transmission configured to alter a dimension of the adjustable implant. The system includes an external adjustment device configured for placement on or adjacent to the skin of the subject having at least one magnet configured for rotation, the external adjustment device further comprising a motor configured to rotate the at least one magnet and an encoder. Rotation of the at least one magnet of the external adjustment device effectuates rotational movement of the permanent magnet of the adjustable implant and alters the dimension of the adjustable implant. Drive control circuitry is configured to receive an input signal from the encoder.