The ? (delta) scale is a non-octave repeating musical scale. It may be regarded as the beta scale's reciprocal since it is, "as far 'down' the (0 3 6 9) circle from ? as ? is 'up.'" As such it would split the minor second into eight equal parts of approximately 14 cents each Play (help·info). This would total approximately 85.7 steps per octave.
The Bohlen-Pierce delta scale is based on the tritave and the 7:5:3 "wide" triad ( Play (help·info)) and the 9:7:5 "narrow" triad ( Play (help·info)) (rather than the conventional 4:5:6 triad). Notes include: