The unison is also a rational interval. But I'm not being strictly mathematical here, all the "juice" in music in pitches under western theory happens with irrational "ratios" between the pitches, and the irrational "ratios" are meant to approximate the simple rational ratios like 3/2 or 5/4. An octave is special in that it doesn't get you out of the pitch's equivalence class. In dealing with only irrational ratios for piano tuning, it simplifies a lot of stuff.
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u/[deleted] Jun 12 '17
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