Finding the right fit for your shoes is not that difficult. All you need to do is take a short walk through the store in the new pair. Squeezing the front end of the shoe, or sliding the index finger behind the heel is another common practice. But back in the 1920s through the 50s, many shoe stores across America and Europe had live x-ray viewing machines, like those in airports for checking luggage, only smaller. These machines clearly showed the bones and flesh of the feet as well as the outline of the shoes, eliminating all the guesswork and allowing customers to choose better fitting shoes. They were also a nice sales gimmick.
Front and side view of a Shoe Fitting Fluoroscope. Photo credit: Wikimedia