that button is actually a bar or flat plate that slides so it will play two different keys which is nice for stepping Actually I knew it caused a mechanical part to move, but I didn't know what else to call it but a button. I found it. On the outside of the case, it says: Koch-Harmonica, CHROMATIC, Made in Germany On the Harmonica itself, it says, THE "CHROMONICA" (chromatic harmonica) Made by M. HOHNER Germany It's in "C" I also have a little "Blues Harp" made by the same company. Also in "C" Did it ever get you any lovin' from the girls? LOL Phil