8:5 · 8 semitones
Minor sixth. Undercharged by about 14 cents: the major third's bill with the sign flipped.
- Pure
- 813.69¢
- Tempered
- 800¢
- Charge
- −13.69¢
- Beat
- 2.77 Hz
Lower note 220 Hz. Pure upper 352.00 Hz. Tempered upper 349.23 Hz.
A minor sixth and a major third add up to an octave, and the octave is never charged. So whatever the keyboard adds to the third it must take from the sixth. The 8:5 ratio is 5:4 turned over, and the tempered sixth is about 13.7 cents flat of it, the same size as the third's charge.
That makes this the third read upside down, and it sounds it. Play "both" and the pulse is about 2.8 a second, against 2.2 for the major third on the same lower note: the same cents of error beat faster when the notes sit higher. It is the same defect, heard from the other end of the octave. Minor sixth (Wikipedia, CC BY-SA).