In 1954, MacCready pointed out the advantages of an Audio Variometer, "There is much to be gained if the variometer indication is presented to the pilot by sound. More than any other instrument except during blind flying, the variometer must be watched continuously. if the pilot can get the reading by ear, he can improve his thermal flying by watching nearby gliders, and he can materially improve the overall flight by studying the cloud formations to be used next."[1]