This AGARDograph is the 8th of the AGARD Flight Test Instrumentation Series and concentrates on the flight test instrumentation for determining the position of movable aircraft components such as rudder, elevator and aileron surfaces, wing flaps, trim tabs, speed brakes, spoilers, power-control levers, elements of nosewheel-steering systems and of landing gear mechanisms, etc. The sensitivity and frequency responses of the various systems used for making these measurements are discussed in the following groups with examples potentiometers, synchros, inductive systems, and digital systems.