Background
Biosig Instruments held a patent on a heart rate monitor designed for use with exercise equipment. The device used a pair of electrodes spaced apart on a handlebar grip to detect heart rate signals while filtering out electrical noise caused by the user’s muscular activity (electromyogram signals). The key claim language required that “live” and “common” electrodes be in a “spaced relationship with each other” — a phrase intended to describe the physical separation between the electrodes necessary for the device to work properly. Nautilus, a maker of exercise equipment, allegedly incorporated similar heart rate monitoring technology and was sued for infringement.
The district court held that “spaced relationship” was indefinite — it did not specify how far apart the electrodes should be, or provide any numerical or functional criteria for determining the required spacing. Without that guidance, the district court concluded, a skilled artisan could not determine the scope of the claim. Biosig appealed to the Federal Circuit, which applied the then-prevailing standard that a patent claim is indefinite only if it is not “amenable to construction” or is “insolubly ambiguous.”
The Court’s Holding
The Federal Circuit reversed the district court’s indefiniteness finding and held that “spaced relationship” was definite. The court applied its “insolubly ambiguous” standard: even if the phrase does not specify an exact measurement, it is not indefinite if a skilled artisan could determine its meaning in the context of the patent. The court found that the specification, the claims, and the functional context (the electrodes must be spaced far enough apart to capture both heart rate signals and eliminate muscle noise, but not so far apart as to fail to function) provided sufficient guidance. A skilled artisan could understand the required spacing through experimentation and understanding of the device’s technical operation.
Nautilus petitioned the Supreme Court for certiorari, and the Court granted it to address the proper standard for patent indefiniteness under 35 U.S.C. § 112 ¶ 2.
Key Takeaways
- Under the Federal Circuit’s 2013 “insolubly ambiguous” standard, claims were indefinite only in extreme cases where no reasonable construction could be ascertained — a very permissive threshold that allowed many vague claims to survive.
- The Supreme Court unanimously reversed in Nautilus, Inc. v. Biosig Instruments (2014), holding that the “insolubly ambiguous” formulation was insufficient and that § 112 requires that claims, read in light of the specification and prosecution history, inform those skilled in the art about the scope of the invention with “reasonable certainty.”
- On remand after the SCOTUS decision, the Federal Circuit applied the new “reasonable certainty” standard and concluded that “spaced relationship” was still definite — even under the tighter test, the functional context of the claim provided enough guidance to a skilled artisan.
- The case established the modern definiteness standard in U.S. patent law: “reasonable certainty” is more demanding than “insolubly ambiguous,” though Biosig itself shows that many claims that survived the old standard can still survive the new one when the specification provides functional context.
Why It Matters
The Biosig/Nautilus saga produced the current legal standard for patent definiteness — the most fundamental rule governing the clarity requirement for patent claims. The old “insolubly ambiguous” test was widely criticized as too permissive: it allowed patents to issue with claims that were genuinely unclear, creating the very patent ambiguity that was supposed to be prevented. The Supreme Court’s “reasonable certainty” standard was designed to raise the bar and improve the public notice function of patent claims.
In practice, the new standard has produced more indefiniteness findings than the old one, particularly for claims with qualitative or relative language (“substantially,” “approximately,” “minimal,” “unobtrusive”) that lack objective anchors in the specification. For patent drafters, Biosig/Nautilus reinforces the importance of providing functional benchmarks, examples, or definitions for any term that could be construed as a term of degree. For patent challengers, the “reasonable certainty” standard has created a viable indefiniteness argument for many claims that might have survived under the prior test.