Abstract: A system for performing target acquisition and tracking under the control a human operator. The system has a slewable sensor with a line of sight and includes apparatus for slewing the sensor to align its line of sight with a target, the difference between the position of the target and the line of sight being a line of sight error. A display displays the line of sight error to the operator at either a first or a second magnification, selectable by the operator. The operator uses a control manipulator to generate input signals and supply them to the rest of the system. Circuitry is provided for automatically switching from proportional to proportional-plus-integral control upon changing from the first to the second magnification. Circuitry is also provided for initializing an integrator prior to the switchover from the first to the second magnification to eliminate control transients in the concomitant switchover from proportional to proportional-plus-integral control.