Gauge, dial type, for use with Airspeed Indicator

An important use of air speed indicators is to enable pilots to avoid flying too slowly which would lead to stalling and loss of lift. This was the first air speed indicator to use the air pressure due to the forward movement of the aircraft to give an indication of speed. It was developed at the Royal Aircraft Factory, Farnborough, and originally calibrated on a motor car. Afterwards it was used on the airships Beta and Gamma, and also on the first BE aeroplane. Two long parallel tubes, one measuring air pressure due to aircraft speed from a forward-pointing fixture and the atmospheric pressure, lead to two chambers separated by a diaphragm. Any difference in pressure in the two tubes moves the diaphragm which operates a spring controlled arm and shifts the pointer.