 The first scientific evaluations of these machines in 1948 immediately sparked concern for radiation protection and electrical safety reasons, and found them ineffective at shoe fitting.Large variations in dose were possible depending on the machine design, displacement of the shielding materials, and the time and frequency of use.Radiation surveys showed that American machines delivered an average of 13 roentgen (r) (roughly 0.13 sievert (Sv) of equivalent dose in modern units) to the customer's feet during a typical 20 second viewing, with one capable of delivering 116 r (~1 Sv) in 20 seconds.