Although there are a great number of reasons an invention may not be patentable, one of the few which is under control of the inventor is sometimes referred to as the "One Year Rule." Among other things, 35 USC 102 provides that a claim will not be allowed to issue as a patent if the invention was "in public use or on sale in this country more than one year prior to the date of the application for patent in the United States."

Although the phrases "public use" and "on sale" have been the subject of numerous court cases, a prudent inventor will be certain to apply for a patent on his or her invention before a year has passed from the time any public use or sale of the invention has occurred. Sending a prototype of your invention to a potential manufacturer or selling a couple units of your invention at a flea market could very well be considered as being "public use" or "on sale" and start the one year clock ticking.