Public use bar refers to a statutory bar that prevents the granting of a patent for an invention that was publicly used or sold in the U.S. more than one year before the application date. For example, single public use of patented computer more than one year before application for patent is filed, even without any profit to inventor, is sufficient to establish public use bar.
However, experimental testing and demonstration of invention to small group of invited persons is not public use barring patent on application filed after critical date. [Hanson v. Alpine Valley Ski Area, Inc., 1977 U.S. Dist. LEXIS 15855 ( E.D. Mich. 1977)]
It was observed in FMC Corp. v. F. E. Myers & Bro. Co., 384 F.2d 4 (6th Cir. Ohio 1967) that an inventor may use invention for purposes of experimentation to test it or bring it to perfection without concern for statutory public use bar to patent.