Septimal tritone
Encyclopedia
The lesser septimal tritone (also Huygens' tritone) is the interval with ratio 7:5 (582.51 cents). The inverse of that interval, the greater septimal tritone, is an interval with ratio 10:7 (617.49 cents). They are also known as the sub-fifth and super-fourth, or subminor fifth and supermajor fourth, respectively.

The difference between these two is the septimal sixth tone (50:49, 34.98 cents) .
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