I found a Continental Chromatic accordion in an auction and got it for $125. Unfortuneately, I have been unable to master the thing. It looks something like a piano accordion with the standard 120 bass left hand buttons but the right side has what looks like a piano keyboard with the black and white keys but extending out from the end of the white keys are two more rows of stubby white keys. They play chromatically outer white stub, inner white stub, regular white key, black key all being semitones apart and the net semitone up from the black key is the next outer stubby white key up. I am told that the perfect arangement is to have three stubby keys with the regular piano arrangement which makes every musical key have the same fingering. It also shares the piano accordian's same note push or pull. The five-row "BUTTON-KEY" accordion you described is diatonic (different note push/pull) and the arrangement of the left-hand buttons are so that most keys have the same fingering. Jimmy Shand played one of these (and I think so did Dermot O'Brian). Because of the combination of the five rows and the push/pull, you have an octave and a bit within the reach of a relaxed hand (Not the spanned hand you need to get an octave on a piano keyboard), which makes the button key one of the fastest instruments ever invented and highly suited to Scottish and Irish dance music. (Although Phil Cunningham is no slouch on the piano accordion)