2/5-comma meantone

2/5-comma meantone is a tuning of meantone where the fifth is flattened by 2/5 of the syntonic comma, producing a fifth of 693.352 cents; its eigenmonzo is 27/25. This is approximated well by 45edo.

The most accurate choice for extending 2/5-comma meantone into the 7-limit, 11-limit or 13-limit is flattone temperament. In fact, 2/5-comma meantone’s fifth is almost exactly the optimal CTE generator for 11-limit flattone — less than 0.2 cents different.