The School Overhead Projector
A hot fan, an acetate sheet, and a teacher's handwriting in smeary pen.
Before whiteboards and projectors, learning happened via a bright box that hummed and got hot enough to burn.
The acetate rolls scrolled across on a handle. The bulb blew constantly and there was always a spare in a drawer that nobody could find.
A hand in front of the lens made a shadow puppet the size of the wall, which happened in every lesson, in every school, forever.
Cost back then
£200 a unit
Goes for now
Skipped in their thousands; £20 secondhand
