Under the Patent Act, a patent specification must “conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as [the] invention.”1 A patent claim that does not satisfy this requirement, which is called “definiteness,” is invalid.2

Last year the Supreme Court rejected the Federal Circuit’s standard for determining indefiniteness, which required a finding that the claim language is “insolubly ambiguous” and “not amenable to construction.” In its place, the Supreme Court articulated a new standard—claims must “inform those skilled in the art about the scope of the invention with reasonable certainty.”3 Based on the Supreme Court’s newly-articulated standard, commentators suggested that the threshold for satisfying the definiteness requirement had been lowered. In its April 27, 2015, panel decision on remand, however, the Federal Circuit dispelled such a notion by clarifying that the results under either articulation of the definiteness requirement are likely to be the same.4 Here we discuss how the Federal Circuit has applied the Supreme Court’s new indefiniteness standard fromNautilus.


The patent at issue in Nautilus is directed to a heart rate monitor on exercise equipment that operates more accurately than prior systems.5 The asserted claims require, among other things, two electrodes to be “in a spaced relationship with each other” such that the system is able to detect and remove spurious electromyogram (“EMG”) signals from the electrocardiograph (“ECG”) signals (otherwise known as the heart rate). Figure 1 of the patent shows the claimed apparatus, where metal strips 9 and 11 around the tube are an example of the electrodes “in a spaced relationship”:

Click here to view the image.

During reexamination proceedings, the patentee successfully distinguished prior art based on the requirement that the claimed device substantially eliminate EMG signals. Based on declarations from an inventor and an expert submitted during reexamination, the patentee argued that a person of ordinary skill in the art at the time the patent was filed would have known to how to use a standard oscilloscope to determine the dimensions of the device, including the exact distance of the “spaced relationship” that would eliminate EMG signals as required by the claimed invention. The examiner found this claimed function,6 the elimination of the EMG signals from the ECG signal, to be “‘crucial’ as a reason for overcoming the cited prior art and confirming the patentability of the asserted claims upon reexamination.”7


During a summary judgment hearing on the defendant’s indefiniteness motion, the district court issued an oral ruling granting the motion for summary judgment that the “spaced relationship” term was indefinite as a matter of law.8 The district court found that the requirement that the claimed device substantially eliminate EMG signals was “all a description of the desired result and not a description of any invention that is calculated [if] followed to produce that result and, therefore, violates the requirement of specificity in Section 112.”9 Essentially rejecting the expert report submitted during briefing and the declarations submitted in the reexamination record, the district court found on summary judgment that a person of ordinary skill in the art at the time of the invention, after reading the patent, would not have known how to design the claimed system with electrodes spaced at a distance apart such that the circuitry is able to eliminate EMG signals.


On appeal, the Federal Circuit reversed, holding that the intrinsic evidence provides sufficient clarity for the term “spaced relationship.”10 Relying on its precedent that a term is indefinite “only when it is not amenable to construction or insolubly ambiguous,” the Federal Circuit found that the claim language, specification, and the figures illustrated that the “spaced relationship” was something less than the width of a user’s hand and greater than infinitesimally small.11

A majority of the panel (Judges Wallach and Newman) also concluded that the functional requirement recited in claim 1, that the system substantially eliminate EMG signals, “sheds further light on the meaning” of the “spaced relationship” term. The majority cited the inventor and expert declarations made during reexamination, whereby the patentee successfully distinguished prior art based on the claim’s requirement that the system substantially eliminate EMG signals.

In concurrence, Judge Schall stated that the panel should not have addressed the functional limitation, but should have instead stopped its analysis after concluding that the claim language, specification, and the figures illustrated that the “spaced relationship” was something less than the width of a user’s hand and greater than infinitesimally small.


On certiorari, the Supreme Court found that the legal test for indefiniteness used by Federal Circuit’s test “can breed lower court confusion.” The Court held that under 35 U.S.C. § 112 ¶ 2,12 “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 about the scope of the invention.”13 This new standard articulated by the Court is meant to “mandate[] clarity, while recognizing that absolute precision is unattainable.”14 Ultimately, the Court declined to address the validity of the patent-in-suit, remanding for the Federal Circuit to decide the case employing the new prescribed standard.15


Back in front of the same panel on remand, the Federal Circuit again reversed the district court’s decision on essentially the same grounds articulated in its prior opinion.16 After a review of precedent on the meaning of “reasonable certainty,” the Federal Circuit all-but concluded that the new standard articulated by the Supreme Court did not render prior precedent inapplicable.17 Suggesting that the new standard would not substantively change the analysis, the Federal Circuit states that the Supreme Court “modified the standard by which lower courts examine allegedly ambiguous claims; we may now steer by the bright star of ‘reasonable certainty,’ rather than the unreliable compass of ‘insoluble ambiguity.’”18

Then, invoking the de novo standard of review that is used for review of claim construction decisions that do not involve issues of fact and relying on the claim language, specification, figures, and prosecution history (including statements made during reexamination), the Federal Circuit reiterated that the intrinsic evidence “make[s] clear that a skilled artisan would understand with reasonable certainty the scope of the invention.”19 Interestingly, the entire panel20 of the Federal Circuit reiterated the earlier opinion’s findings that the “spaced relationship” was something less than the width of a user’s hand and greater than infinitesimally small and also that a skilled artisan would understand how to determine the exact spacing based on the functional limitation requiring that the system substantially eliminate EMG signals.21


What is clear from the Federal Circuit’s holding is that it views the Supreme Court’s new standard as not changing the Federal Circuit’s law of indefiniteness considerably, if at all. This outcome should probably not be a surprise, as the Supreme Court predicted as much in its holding, stating that the “Federal Circuit’s fuller explications of the [prior test] we recognize, may come closer to tracking the statutory prescription.”22

One thing that remains unclear from the holding is the roll expert opinions will play in the indefiniteness analysis. Though an expert report was submitted to the district court below, neither the district court nor the Federal Circuit relied on that opinion (extrinsic evidence) in their decisions. Had the district court relied on expert testimony, the analysis by the Federal Circuit may have changed. Because determinations of factual issues on claim construction are reviewed for clear error, even though the ultimate claim construction decision is a legal question reviewedde novo, the analysis of a district court indefiniteness decision that is based on factual determinations should logically be given more deference.23

What would otherwise have been extrinsic evidence in the district court, the inventor’s declaration and an expert report, became intrinsic evidence by virtue of their submission into the record during that patent’s reexamination. Interestingly, the district court decision could be interpreted as rejecting these intrinsic declarations, as not proving that a skilled artisan would have known how to determine the proper spacing. Had they been submitted as extrinsic evidence, instead of incorporated into the intrinsic record during reexamination, the Federal Circuit’s decision regarding the function providing clarity for the claim construction would have, theoretically, had a different result.