5/9-comma meantone

5/9-comma meantone is a tuning of meantone where the fifth is flattened by 5/9 of the syntonic comma, producing a fifth of 690.007 cents. This is approximated well by 40edo, using the 40c val.

The most accurate choice for extending 5/9-comma meantone into the 7-limit or 11-limit is flattertone temperament.