Heptatonic scale are considered subsets of a twelve-pitch scale roughly analogous to the Western chromatic scale. The first and fifth melakarta tones, corresponding to the first and eighth chromatic tones, are invariable in inflection, and the fourth melakarta tone, corresponding to the sixth or seventh chromatic tone, is allowed one of two inflections only, a natural ("shuddah") position and a raised ("tivra") position. The second and third melakarta tones can be picked from the 4 chromatic tones (second through fifth), and similarly for the sixth and seventh. Thus the number of possible forms is equal to twice the square of the number
Hexatonic scale Others have referred to it as the "Promethean chord". Since blue notes are alternate inflections, strictly speaking there can be no one blues scale, but the scale most commonly called "the blues scale" comprises a flatted seventh blue note, a flatted third blue note, and a flatted fifth blue note along with other pitches derived from the minor pentatonic scale: C E F G G B C. The tritone scale, C D E G G() B, is enharmonically equivalent to the Petrushka chord, C C E F G A. The "two-semitone tritone scale", C D D F G A, is