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 (presumably 16:15) into eight equal parts of approximately 14 cents each Play (help·info). This would total approximately 85.7 steps per octave.
The scale step may also precisely be derived from using 50:28 (25:14, 1003.8 cents, A♯, Play (help·info)) to approximate the interval , which equals 6:5 (E♭, 315.64 cents, Play (help·info)). Thus the step is approximately 13.946 cents and there are 86.049 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: