Shoe-fitting fluoroscopes
Foot X-ray machines were prominently featured in many shoe stores

This was basically an X-ray machine operated by the salespeople in a shoe store. Children would put on the chosen shoes and stand on the device with their feet in the slot provided. The shoe salesman, the child, and the child's parent could all then peer into the viewers and see an image of the child's foot and toes and the outline of the shoe. Children apparently had a good time watching while they wiggled their toes. Lots more information on this is available: for instance, see the Oak Ridge Associated Universities site and The Museum of Quackery .