Most patent systems prohibit an inventor from applying for a patent once he has offered the product for commercial sale. There are jurisdictionally specific exceptions to the “on-sale bar,” for example tradeshows and experimental use and some jurisdictions offer limited grace periods, the United States for example twelve months, while Japan offers six months for experimental or academic use.
However, because these exceptions are often hedged with conditions, are different from one country to the next, may only apply to certain international trade-shows and not others, and often simply do not apply at all, inventors should not rely on them. For example the US on sale bar is strictly interpreted, with one Supreme Court case holding that even a sketch on a cocktail napkin of a proposed design when given to the customer amounts to a breach. Rather they should assume that a patent should always be applied for before a product is offered for commercial sale or use, advertised, or presented at a trade show. An exception exists for Experimental Use, i.e., testing of the invention.