The ? (beta) scale is a non-octave-repeating musical scale. In one version, it splits the perfect fifth (3:2) into eleven equal parts of 63.8 cents each. Another interpretation splits the perfect fourth into two equal parts, or eight equal parts of approximately 64 cents each Play (help·info). This totals approximately 18.8 steps per octave. It may be derived from using 11:6 Play (help·info) to approximate the interval , which equals 6:5 Play (help·info).
Although neither has an octave, one advantage to the beta scale over the alpha scale is that 15 steps, 957.494 cents, Play (help·info) is a reasonable approximation to the seventh harmonic (7:4, 968.826 cents) Play (help·info) though both have nice triads ( Play major triad (help·info), minor triad (help·info), and dominant seventh (help·info)).