I have an Italian button accordian I bought at a flea market. It has three rows of diatonic buttons on the right. The top two have a little more that two octaves of a chromatic scale starting with C. The bottom has a G scale. The left buttons are the same both in and out and consist of a row of major chords, a row of minor chords, a row of seventh chords, and two rows that seem to be major chords with extra bass notes. It's fairly easy to pick out melodies with the right hand but the potential of the left hand is a little overwhelming.