The Quadrature Oscillograph: An Electromechanical Device Having Two Degrees of Freedom
J.B. Sherman · Proceedings of the IRE · 1935
An electromechanical oscillograph galvanometer has been developed which is capable of deflection along two mutually perpendicular sets of coordinate axes. For power and low audio frequencies, the instrument presents all of the possibilities inherent in a deflecting system of two degrees of freedom.