Roman Numeral Notation

Scale degrees number notes, counted from the tonic. Roman numerals number chords the same way, one built on each degree: I is the major chord on the 1st degree, V on the 5th, and so on.

Case carries the chord's quality: uppercase for major, lowercase for minor. In C major, the 1st degree carries a major triad and the 6th a minor one, so that's shown as I and vi

Another common chord is the diminished triad, shown in its traditional notation as ° next to the Roman numeral, for example vii° is the diminished triad on the 7th degree. See Chord Quality for the full table of chord qualities, their suffixes and their characteristic color in the app

All 7, in one scale

Every major scale produces the same seven triads, a few major and minor triads, and one diminished chord at the 7th degree, i.e. the sequence of triads here would be I, ii, iii, IV, V, vi, vii°