Thats interesting Peer, I have a PA on long term loan but have never been bothered to play it, so you can pick out single piano key notes and it corresponds?
Might be a good way for me to start messing with it.
The white keys on a PA, piano, keyboard, whatever, correspond to the notes on an C accordion.
So you can figure out what you can do on a CA and what you can't. Not necessarily in C but of course also in G, and Dm, Am and F are also possible to some degree.
Of course you can figure this out on a C box rightaway, but a keyboard offers a fresh point of view. Litterally, because now you can see all the notes on the keyboard. No black keys. No pushing and pulling. Easy!
Any song or tune playable on those white keys is possible on a CA. Of course, for other keys you need a different box, but the idea stays the same.
I hope this makes any sense!