Hi,
With help from me, my daughter made a simple listing to draw with keys R/F (up/down) and N/M (left/right) - we then added C to clear. She became concerned that she couldn't see where the pixel block was, so press W to 'wink' - line 102 is a simple way to slow the wink down slightly without a lot of renumbering that I added as it was too fast otherwise.
It's here for prosperity. I remember writing similar listings on the ZX81, and more optimised ones though she's not advanced enough into BASIC to start worrying about optimisation yet.
My conclusion is that the ZX81 is *still* a good enough learning machine in some instances, though she did ask about adding colour. I had to explain that we didn't have colour back in the 1980s and everyone's vision was in black and white anyway
Regards,
Shaun