81/70
| Ratio | 81/70 |
| Monzo | [-1 4 -1 -1⟩ |
| Size in cents | 252.6804 |
| Name(s) | septimal semiaugmented second, septimal ultramajor second |
| Color name | rg2, rugu 2nd |
81/70, the septimal semiaugmented second or septimal ultramajor second is a 7-limit interseptimal ratio of about 253 cents. It is sharp of a subminor third 7/6 by a sensamagic comma 245/243, and sharp of a major second 16/9 by a septimal quartertone 36/35.
It is also sharp of a minor third 6/5 by a subminor second 28/27. For this fact it is useful in the Canovian chord and provides the function of a voice leading up to the minor third.
The interval is so perfectly approximated by 19-edo, with an error of 0.05 cents. There are a number of edos that do this equally well, 171-edo to name one. The first edo that does this better than 19-edo with patent val is 660-edo.
See also
- 140/81, its octave complement
- Gallery of just intervals
