Abstract: An on-board take-off performance indicator system for an aircraft includes a ground-engaging wheel which measures distance run during take-off and moves the slider of a selected one of a bank of potentiometers in response thereto. Each potentiometer is wound in accordance with a respective defined speed/distance characteristic. The selection of the potentiometer can be completely manual but is preferably in response to an electrical analogue of a graphical method which takes account of parameters individual to a particular take-off. An indication of expected speed in view of distance run is provided by the potentiometer output by means of an index on the airspeed indicator in the aircraft.