The f00ter is designed & produced to the same accuracy as the RITZ Stick which is the original US foot measure device. It's the standard that all other devices have been copied from. Many shoe manufacturers don't produce or label their shoes to properly conform to the US Standard Sizing. If you properly use the f00ter to size your feet and find the shoes you bought don't fit properly, it is because the shoe is the wrong size, not the measurement from the f00ter.