Abstract: Apparatus for correcting or compensating for the tracking error of the pivotally mounted (1) tone arm (23) of a phonograph includes a first intermediate member (9) to which said tone arm (23) is pivotally (1) connected, a second intermediate member (12) which is rotatably connected to the first intermediate member (9) by a belt (18) and pulleys (13) which are sized in such a way that a photodiode source (21) and a photodiode detector (22) both carried by the second intermediate member (12) will tend to be indirectly moved by a motor to maintain them substantially constantly in register with a point on the tone arm (23). A slotted mask (24) carried by the tone arm (23) is interposed between the source (21) and the detector (22) and its slot defines a central "null" position in which said motor will not be driven when the required relationship exists. Deviation in either direction will cause the motor to be driven to re-establish this relationship. An insignificant maximum tracking error below 0.1.degree.

Abstract: A phonograph has a viscous damping arrangement coupling a pick-up arm to the base of the phonograph to damp vertical and horizontal vibrations of the arm. The damping means is coupled to the arm at a position close to the pick-up cartridge of the arm. A counter-balance mass is also provided on the arm, the mass having an adjustable position and mass.

Abstract: Gramophone turntable apparatus comprises a turntable with a hydrodynamic bearing so that, on rotation, the turntable is supported solely by a pressurized film of fluid. The bearing also supports the rotatable part of a turntable drive motor of rotary or linear form.

Abstract: A control system for a grinding machine or other machine tool, wherein desired workpiece profiles are stored in a digital computer which controls the position of a tool in relation to a workpiece in accordance with the stored profile and in accordance with the position of a workpiece profile follower to compensate for tool wear.

Abstract: A machine for forming gears and the like comprises a workpiece support continuously rotatable about a first axis, a tool support angularly displaceable about a second axis and constructed to support a tool for rotation about a third axis angled to the first axis and an electrical master-slave servo system having a master providing a first electrical signal defining a required angular displacement for the tool support and a second electrical signal for influencing the continuous rotation of the workpiece support in dependence upon the angular displacement defined by the first signal.