4/9-comma meantone

4/9-comma meantone is a tuning of meantone where the fifth is flattened by 4/9 of the syntonic comma, producing a fifth of 692.396649¢ cents. This is approximated well by 26edo (15\26 is 692.307692¢, which is flatter by 0.088957¢, for a cumulative error of only 2.312882¢ for proceeding all the way around the 26edo circle of fifths). The eigenmonzo is 2500/2187 (231.569849¢), which is only a ragisma (4375/4374, 0.395756¢) sharp of 8/7 (231.174094¢).

The most accurate choice for extending 4/9-comma meantone into the 7-limit, 11-limit or 13-limit is flattone temperament.