A brief history of classroom overhead projectors — much more interesting than you’d expect. (Version History / The Verge)
Overhead projectors were one leg of the multimedia trinity for 1970s classrooms. The other two legs were the filmstrip and the 16-mm film projector, the latter used to project educational films from the 1950s that looked old-fashioned and ridiculous in ways that I don’t think educational videos from the 2000s would look to kids today.