2/9-comma meantone

2/9-comma meantone is a meantone tuning which flattens the perfect fifth by 4.779 cents (2/9 of a syntonic comma). This results in a fifth of 697.176 cents.

2/9-comma meantone was described by Lemme Rossi in Sistema musico ouero Musica speculativa (1666), and again by Moritz Wilhelm Drobisch in Über musikalische Tonbestimmung und Temperatur (1852). Of all the known historical temperaments, it is the closest to the optimal 5-, 7-, 11- and 13-limit CTE tunings for meantone.