The idea was this; you visited a shoe shop, tried on a pair of shoes, then put your newly shod feet into the slot at the bottom of the wooden monstrosity, in order to see how well they fitted. All this thanks to vicious X Rays that were bombarded at your feet.
Of course, as children, we would wander in and out of shoe shops all day long just to see X Ray images of our feet. But it wasn't long before Health-n-Safety heard about them, and they were subsequently banned. However, my feet do still glow in the dark; it's a bloody miracle they haven't fallen off!