The Basics of 102(b)
35 U.S.C. 102(b) has some similarities to 102(a). It states that a "person shall be entitled to a patent unless the invention was patented or described in a printed publication in this or a foreign country or in public use or on sale in this country, more than one year prior to the date of the application for patent in the U.S."

Pay special attention to the absence of the word "by others" and the addition of the phrase, "more than 1 year prior to the date of the application". If you put all this together, 102(b) will bar an applicant from gaining a patent on his or her own work in instances where the prior art date was more than 1 year from the date of the application.

Inventors must take care not to let their inventions get out. In addition, if an inventor decides to patent their invention in a foreign country first, they had better quickly get their ducks in a row for a U.S. filing. Otherwise, their application may be rejected under 102(b).

Note that prior art under 102(b) includes patents or printed publications filed anywhere in the world, but the public use or sale must have occurred in the U.S. So technically, an inventor could sell his new invention in Mexico and still be eligible to gain a U.S. patent provided no one steals his idea and claims it as their own before he gets around to patenting it.

The Details of 102(b)
As for public use, all it takes is for just one person to use the invention for the bar to hold. In addition, if the invention is used or sold, even if it is hidden away from view, the inventor will be barred from gaining the patent.

The PTO is just as strict about the on-sale bar. A single sale or even a single offer to sell may bar a patent. The offer to sell doesn't even have to be made public. And, offers for sale that took place in the U.S. may form a statutory bar even if the invention was actually used in a foreign country. To make matters worse, a patent may be barred even if the inventor did not know that the invention was placed on sale in the U.S.

As for use and sale, remember that an inventor may offer to sell the rights to his or her invention through an assignment. What we are talking about here in 102(b) is actually different. The type of sale that provokes the on-sale bar is one that involves selling the actual product or invention. Note that it is also OK to perform experimental testing on the invention, but that experimental testing may only be performed until the invention has been perfected