Biosig Instruments was granted a patent for a heart rate monitor that reduces noise during the detection of heart rate. Upon being sued for patent infringement, Nautilius filed a motion for summary judgment to have the patent invalidated for indefiniteness.

The district court found that the claimed invention “is not a description of any invention but a desired outcome, therefore, violates the requirement of specificity in Section 112”. The district court also found that, “a person of ordinary skill in the art at the time of the invention, after reading this patent would not have known how to design the claimed invention”. Biosig appealed the district court’s decision granting Nautilus’s motion.

On appeal, the Federal Circuit reversed and noted that when “a claim limitation is defined in functional terms, determining whether the limitation is sufficiently definite depends on the disclosure in the specification and the knowledge of a person of ordinary skill in the art.” The Federal Circuit also cited the precedent that “a claim is indefinite only when it is ‘not amenable to construction’ or ‘insolubly ambiguous.’”

The Federal Circuit held that under the rule of U.S.C.§ 112, a patent is invalid for indefiniteness when those of ordinary skill in the art, having read the patent specifications and see into the prosecution history, would not be able to identify the scope of protection.

Using this standard, Federal Circuit determined that the patent survived indefiniteness review. Supreme Court granted certiorari, rejecting this standard and vacated and remanded the case.