Johnston–Copper notation
Based on Johnston's ideas but extended by means of key signatures, this is the notation used by William Copper in the works composed by the techniques of intonalism
Johnston takes as a just intonation basis the staff notation without accidentals (white keys on the piano) so that there are three 4:5:6 chords (F major, C major, and G major). Copper extends this system so that the same three 4:5:6 chords are transposed according to a key signature. In the key of C major, the Johnston and Copper systems are the same. In the key of one sharp, G major, the three 4:5:6 chords are changed so that the basis of just intonation becomes C major, G major, and D major. Any note found in this basis and not altered by a special accidental is tuned according to 5-limit just intonation: the third of the triad, or the '5' of the 4:5:6 chord, is a pure major third from the root; the fifth of the triad is a pure perfect fifth from the root.
Beyond the unaltered basis associated with any key signature, individual notes may be altered by means of accidentals. The standard sharp, flat, and natural signs have the same effect as in common practice notated Western music. A sharp put before a note will either take that note out of the diatonic system indicated by the key signature, or return a note into the diatonic system. For example in C major, the sharp before an F makes the note F#, out of the basis of the key. In G major, where the F is already a sharp as defined by the key signature, the sharp may be used to indicate a return to the key signature if the prior measure of notated music used a different notation, or if the complexity of the music requires a cautionary indication that this note is indeed to be F #. All this is just as in common practice.
When the music demands a note to be tuned differently than the 'basis' then special accidentals are used: an altered sharp sign, an altered flat sign, two altered natural signs (up and down) and two neutral signs (up and down). In Johnston-Copper Notation each such change is exactly a comma, the specific comma indicated by the ratio 81/80 and often called a Syntonic comma .