http://patentlyo.com/patent/2014/06/reasonable-certainty-regarding.html
Through a series of cases, the Federal Circuit has implemented was arguably a stiff test of indefiniteness – making it quite difficult to find a claim invalid as indefinite. As the Supreme Court writes:
According to the Federal Circuit, a patent claim passes the §112, ¶2 threshold so long as the claim is “amenable to construction,” and the claim, as construed, is not “insolubly ambiguous.”
In its opinion here, the Supreme Court found that the insolubly ambiguous fails to apply the statutory requirement noted above. In its place, the court has created a new test as follows:
A patent is invalid for indefiniteness if its claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty, those skilled in the art [at the time the patent was filed] about the scope of the invention. . . . .
The standard we adopt accords with opinions of this Court stating that “the certainty which the law requires in patents is not greater than is reasonable, having regard to their subject-matter.” Minerals Separation, Ltd. v. Hyde, 242 U. S. 261, 270 (1916). . . .
