A closed-loop negative feedback system to be used for controlling the position of a load has a differential amplifier with transfer function K, operating a motor with transfer function 1/(sL + R). The output of the motor operates a gear system with gear ratio N and this, in turn, operates a screw with transfer function 1/s to give the resulting displacement. The position sensor is a potentiometer and this gives a feedback voltage related to the position of the load by the transfer function K. Derive the transfer function for the system as a whole, relating the input voltage to the system to the displacement output.