@thomasfuchs OMG! Saw you previous posts. Only now do i realize that the box fits into a homecomputer, the TI-4A (as i remember it). But it's the same! I had one. I used it. Never knew about the expansion box :( It's in a box somewhere. It sat in my parents attic for some years where lots of pollen got stuck to it and ruined it's appearance.
I got it on a computer-fair when a "dude" realized i could actually write software. I was 13. Ha!