Abstract: A hydraulically driven mill screw-down including an optical encoder directly coupled to the hydraulic drive for producing digital signals representative of motion and direction of motion of the movable roll, a bidirectional counter for maintaining a cumulative count representative of roll position, a pulse source, a bidirectional reference counter for maintaining a count representative of desired roll position, a digital subtractor for producing a difference signal, an analog-to-digital converter for producing an analog signal proportional to the digital difference signal, a servo amplifier and a continuously variable hydraulic valve for controlling the application of fluid pressure to the hydraulic screw-down apparatus. Also disclosed is an emergency stop preset register for dumping an emergency stop desired position into the reference counter when actuated.