The magnets' pole pieces: a sharp edge over a grooveOven (left), speed wheels, pinholes, three magnets, glass plate (right)Dots on the glass: one silver atom eachSilver atoms fly from the oven through a magnet that is stronger at its sharp top edge, so each tiny atomic magnet gets pushed up or down. Every atom lands in one of two spots, never in between. Keep one spot and ask a sideways magnet: it splits 50/50, and asking up-or-down again gives 50/50 too, because each new question erases the last answer. Sideways spreads are drawn 8× larger than life; the 1922 machine had one magnet, and the chain of three is the textbook version of the idea.