An inventor loses the right to a U.S. patent if the invention is used in public in the U.S. more than one year prior to his/her U.S. filing date [35 U.S.C 102(b)]. This usually occurs when the inventor uses the invention in public in the U.S. over a year before the inventor files in the U.S. It can also occur when someone else (who may or may not have independently invented the same invention) uses the invention in public over a year before the inventor files in the U.S. This sort of delay is fatal and results in a "statutory bar" to patentability.
It is important to note that the act (use of the invention in public) can be performed by anyone. It must, however, occur in the U.S (or in its possessions or territories) and before a specific date. That date is one year before the earliest effective filing date of a provisional or nonprovisional (regular) U.S. patent application or an international (PCT) application that designates the U.S. As far as application of this rule is concerned, it matters not what the date of invention is or that the inventor(s) can claim priority of invention based on the filing date of a non-U.S. (national or regional) patent application. Only the U.S. filing date (which can be the same as the PCT filing date) is considered. Public use in other countries, e.g., in World Trade Organization (WTO) or North American Free Trade Agreement (NAFTA) member countries, does not invoke the bar.
The public use can be a single public use of a single article by a single person. Public use or public accessibility of a machine that embodies the invention invokes the bar, even if the invention is a part of the machine that is hidden from view. Public use also occurs when the inventor allows another to use an invention without restriction or obligation of secrecy to the inventor. Making a product of a secret machine or process accessible to the public can be a public use of the machine or process if "how to make" and "how to use" the machine or process are ascertainable by inspection or analysis of the product. Patent Partner explains the experimental exception to this rule in another evaluation element.