An automatic control system used in aircraft,
motor cars, and other complex machines. A
specific input, such as moving a lever or
joystick, causes a specific output, such as
feeding current to an electric motor that
moves, for example, the rudder of the
aircraft. At the same time the position of
the rudder is detected and fed back to the
central control, so that small adjustments
can continually be made to maintain the
desired course.