That link appears to be broken. While searching around there a bit, I did learn how an etch-a-sketch works.
The describe it as:
"An Etch-a-Sketch® is actually a pretty amazing device! It is
essentially a manually operated plotter with a built-in erasing system.
Anyone who has used an Etch-a-Sketch before will recognize the familiar
red plastic toy with the glass drawing window (now also available in
other fashion colors):"
which would not be my description of it. The funny thing is that when you think back to my day, we were pretty easily entertained. Give me an Etch-a-sketch and a Slinky and I could be entertained for days on end.