this angular interpretation of intervals is helpful to visualize a very practical example of multiplication in music: euler-fokker genera used in describing the just intonation tuning of keyboard instruments . each genus represents an harmonic function such as "3 perfect fifths stacked" or other sonority such as { c g d f }, which, when multiplied by the correct angle(s) of copy, approximately fills the 12tet circumferential space of the circle of fifths. it would be possible, though not musically pretty, to tune an augmented triad of two perfect non-beating major thirds, then (multiplying) tune two tempered fifths above and 1 below each note of the augmented chord; this is euler-fokker genus [555]. a different result is obtained by starting with the "3 perfect fifths stacked", and from these non-beating notes tuning a tempered major third above and below; this is euler-fokker genus [333].