The book deals with the practice of stabilizing servomechanisms. He contributed to the theory of servomechanisms and feedback control systems. The principles developed were applied to design problems of servomechanisms and other feedback control systems. A servo drive is a special electronic amplifier used to power electric servomechanisms. IBM was one of the subcontractors, as was MIT, which took care of the servomechanisms. The endoskeleton is actuated by a powerful network of hydraulic servomechanisms, making Terminators superhumanly strong. The endoskeleton is actuated by a powerful network of electric servomechanisms, making Terminators superhumanly strong. PWM is used to control servomechanisms; see servo control. The autopilot was further developed, to include e.g. improved control algorithms and hydraulic servomechanisms. CNC lathes use computers and servomechanisms to regulate the rates of movement. Positioning servomechanisms were first used in military fire-control and marine navigation equipment. Electrical servomechanisms were used as early as 1888 in Elisha Gray's Telautograph. In 1933 Brown's servomechanisms were displayed at the Century of Progress World Fair. Her group used the Servomechanisms Labs analog correlation computer, built by Norbert Wiener. Modern servomechanisms use solid state power amplifiers, usually built from MOSFET or thyristor devices.