Feed back

General principle where by the results produced in an ongoing reaction become factors in modifying or changing the reaction;negative feed back is the principle used in self-regulating control systems from a simple thermostat and stream -engine governor to automatic computer controlled machine tools .A fully computerized control system ,in which there is no operator intervention is called a closed-loop feed back systems >asystem that also responds to control signals from an operator is called an open loop feed back systm.