U.S. Patent Specifications

An aircraft instrument comprising a casing, a weight movable for a small distance between an upper and a lower stop in said casing, means for causing a pressure differential to be applied to said weight thereby tending to force it against one of said stops, means for mounting said casing in an aeroplane so that acceleration acting on the aeroplane will tend to force said weight against the lower stop, an electric switch operated by a small motion of said weight, a spring acting against said weight and tending to hold it against said upper stop, the closing of said switch being accomplished by the action of acceleration against the differential pressure and said spring.