I found this cheap plastic sketch tablet at an outdoor market in former East Berlin in 1992. It's the kind where you use the stylus and draw on the film to make an image. Sigmund Freud wrote about this object — officially called a "Wunderblock." He used it as a metaphor to explain psychological trauma; you can lift the film and erase the drawing but imprints from the pressure of the stylus will always remain on the pad beneath it.

Some child had already tried it out but hadn't bought it. I bought two. One in a green frame that has never been drawn on and this red framed one with its home-made Donald Duck, drawn from memory.
I will never lift up the film.