Etch A Sketch
Etch-A-Sketch is a licensed toy sold by the Ohio Art Company. It was invented in 1959 as a prototype by Arthur Granjean who called it "The Magic Screen". After Ohio Art bought the rights to develop the invention, it debuted commercially in 1960.
The classic children's toy is relatively flat and rectangular, looking somewhat like a small television screen. It is typically red in color with two large white knobs, although other styles and colors are now available.
The toy works as a simplified version of a plotter. The inside surface of the glass screen is coated with fine aluminum 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. To erase the picture, one simply turns the toy upside down and shakes it back and forth several times; this coats the glass surface once again with aluminum powder. (The powder actually contains small aluminum beads to enable it to flow better.)
It is notoriously difficult to create straight diagonal lines or smoothly curved lines with an Etch-A-Sketch. One solution is to carefully alternate horizontal and vertical lines in very small increments, a technique somewhat reminiscent of how such lines are drawn by raster-scan computer displays. Circles are also extremely difficult to draw on the toy.