Biosig Instruments, Inc. (Biosig) holds U.S. Patent No. 5,337,753 (the 753 patent), which relates to a heart rate monitor on exercise equipment. In 2004, Biosig sued Nautilus, Inc. (Nautilus) alleging that Nautilus infringed several claims of the 753 patent.

In its claim construction, the District Court focused on claim language regarding electrodes “mounted…in spaced relationship with each other.” While it was understood that there must be some minimum distance between the electrodes, the patent provided no indication of what was the proper spacing.

Nautilus moved for summary judgment on (1) whether there was infringement and (2) whether the patent was invalid due to its vagueness. The District Court denied Nautilus’ motion as to the issue of infringement but granted the motion as to the issue of the patent’s invalidity.

Biosig appealed to the U.S. Court of Appeals for the Federal Circuit, which reversed the District Court’s decision. In makings its determination, the Federal Circuit applied the then-current standard, wherein a claim may be indefinite “only when it is ‘not amenable to construction’ or ‘insolubly ambiguous.”

Applying the “insolubly ambiguous” standard, the Federal Circuit found that the term “spaced relationship” was definite, in view of the claim language, specification, and prosecution history. It held that there was some minimum distance, greater than zero, that was also less than the size of a person’s hand, since one hand must touch the two electrodes.

The United States Supreme Court granted certiorari and reversed and remanded the Federal Circuit’s holding. The Court recognized that while absolute precision may not be possible, the definiteness standard mandates clarity. The “insolubly ambiguous” standard would allow a patent to make verbal sense while failing to provide the public with sufficient notice of the claimed invention.

The Court unanimously held that a patent is invalid for indefiniteness if its claims, read in light of the patent’s specification and prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention.


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