Ditone means literally "two tones", and refers to an ancient Greek musical interval equivalent to today's major-3rd. In the standard pythagorean tuning it is composed of two tones each of ratio 9:8 and 2,3-monzo [-3 2>, thus the ditone has ratio 81:64 and 2,3-monzo [-6 4> = ~407.82000346155 cents.