The toy is a kind of plotter.
The inside surface of the glass screen is coated with aluminium powder, which is then scraped off by a movable stylus, leaving a dark line on the light gray screen.
The stylus is controlled by the two large knobs, one of which moves it vertically and the other horizontally.
Turning both knobs simultaneously makes diagonal lines.
To erase the picture, the user turns the toy upside down and shakes it.
Doing this causes polystyrene beads to smooth out and re-coat the inside surface of the screen with aluminum powder.
The "black" line merely exposes the darkness inside the toy.
Scraping out large "black" areas allows enough light through to expose parts of the interior.
The toy is a kind of plotter. The inside surface of the glass screen is coated with aluminium powder, which is then scraped off by a movable stylus, leaving a dark line on the light gray screen. The stylus is controlled by the two large knobs, one of which moves it vertically and the other horizontally. Turning both knobs simultaneously makes diagonal lines. To erase the picture, the user turns the toy upside down and shakes it. Doing this causes polystyrene beads to smooth out and re-coat the inside surface of the screen with aluminum powder. The "black" line merely exposes the darkness inside the toy. Scraping out large "black" areas allows enough light through to expose parts of the interior.
Etch A Sketch