Simply put, it's a diagram that lays out the relationship between every musical note, key, ... For example, to change key from G major to A major, find the new key’s root (A) on the circle, and the ...

Thus Coltrane’s circle shows those same 12 semitones and their notations (flat or sharp). The outer ring portrays the hexatonic or whole-tone scale of the note Do, and the inner ring portrays ...