Beginning in the 1960s, Johnston had proposed an approach to notating music in just intonation (see Just intonation), redefining the understanding of conventional symbols (the seven "white" notes, the sharps and flats) and adding further accidentals, each designed to extend the notation into higher prime limits.
Though, "this notation is not tied to any particular diapason", and "what remains constant are the ratio relations between pitches", "most of his works utilize A = 440 as the tuning note", making C 264 Hertz .