This app enables users to choose, though it depends on parameters, one of the most consonant chord candidates that can be placed between the previous chord Y and the following chord Z amongst the entire chords. It also enables users to examine all sorts of consonant/dissonant degree that happens in chord progressons. I fully take advantage of the latest music theory that perfectly matches musical set theory. And I am very sure that this is the very first app in the world that musical set theory is applied to chord progression or music modulation, in other words, tonal music. And chord progressions this calculation system can produce is so incredible.