7-limit tuning

Harmonic seventh, septimal seventh
Septimal chromatic semitone on C
A 9/7 major third from C to E7 upside-down resembles a supermajor third or blue note.
Septimal minor third on C

7-limit is a musical tuning where the largest prime number factor of the interval ratios between pitches is seven. The only primes available in septimal tuning are 2, 3, 5, and 7. Limit is a term devised by Harry Partch.