A patent model was a handmade miniature model no larger than 12" by 12" by 12" (approximately 30 cm by 30 cm by 30 cm) that showed how an invention works. It was one of the most interesting early features of the United States patent system. Since some early inventors had little technological or legal training, it was difficult for them to submit formal patent applications which require the novel features of an invention to be described in a written application and a number of diagrams.