Septimal whole tone

[6] It can also be thought of as the octave inversion of the 7/4 interval, the harmonic seventh.

No close approximation to this interval exists in the standard 12 equal temperament used in most modern western music.

The very simple 5 equal temperament is the smallest system to match this interval well.

26 equal temperament matches this interval almost perfectly with an error of only 0.4 cents, but at the cost of the significant flatness of its major thirds and fifths.

31 equal temperament, which has much more accurate fifths and major thirds, approximates 8/7 with a slightly higher error of 1.1 cents.