Patents

Grace Instrument v. Chandler: When the Specification, Not the Dictionary, Decides Definiteness

The Federal Circuit revived an oil-well viscometer patent by holding that a term of degree must be measured against the intrinsic record before a court reaches for a dictionary — while affirming a separate means-plus-function construction.

March 24, 2026
A laboratory viscometer instrument used to measure fluid viscosity
The patent claimed a viscometer with an 'enlarged chamber'; whether that term was definite turned on the patent's own teaching, not a dictionary. Shutterstock
Educational content, not legal advice. This article explains general legal concepts. It does not create an attorney–client relationship. For your specific situation, consult a licensed attorney.

Grace Instrument Industries, LLC v. Chandler Instruments Company, LLC, No. 2021-2370 (Fed. Cir. Jan. 12, 2023), is a compact but instructive lesson in how the definiteness inquiry of 35 U.S.C. § 112 actually runs. A panel of Judges Chen, Cunningham, and Stark — Judge Chen writing — reviewed a claim construction order from the United States District Court for the Southern District of Texas (No. 4:20-cv-01749, Judge Andrew S. Hanen) that had simultaneously sunk one claim term and salvaged another. The district court found the term “enlarged chamber” indefinite and construed the means-plus-function term “means for driving said rotor to rotate located in at least one bottom section.” On the strength of those rulings the parties stipulated that the asserted claims of U.S. Patent No. 7,412,877 were invalid or not infringed, and judgment entered for Chandler. The Federal Circuit vacated the indefiniteness holding on “enlarged chamber” and remanded, while affirming the construction of the means-plus-function term. The case is a clean illustration of two § 112 doctrines pulling in opposite directions in the same opinion.

At a glance

  • Case: Grace Instrument Industries, LLC v. Chandler Instruments Company, LLC, No. 2021-2370 (Fed. Cir. Jan. 12, 2023)
  • Below: S.D. Tex., No. 4:20-cv-01749 (Hanen, J.); panel of Chen, Cunningham, and Stark, opinion by Judge Chen
  • Patent: U.S. Patent No. 7,412,877, directed to a liquid-pressurized viscometer that measures drilling-fluid viscosity under simulated down-hole conditions
  • Terms at issue: “enlarged chamber” (definiteness, § 112 ¶ 2 / § 112(b)) and “means for driving said rotor to rotate located in at least one bottom section” (means-plus-function, § 112 ¶ 6 / § 112(f))
  • Holdings: (1) “enlarged chamber” is not indefinite on this record; the district court erred by privileging a dictionary over the intrinsic record — vacated and remanded; (2) the construction of the “means for driving” term, limited to a magnetic-coupling or direct-drive structure and equivalents, is affirmed
  • Standard of review: Indefiniteness is a legal conclusion reviewed de novo; underlying factual findings for clear error; any fact critical to indefiniteness must be proven by clear and convincing evidence

The definiteness requirement of § 112(b)

The second paragraph of § 112 — § 112(b) in its post-AIA form — requires that a patent’s claims “particularly point[] out and distinctly claim[]” the subject matter the inventor regards as the invention. The doctrinal content of that requirement now comes from Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 898 (2014), which the Grace panel quoted directly: 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.” That standard is demanding in theory but forgiving of the ordinary imprecision of language — it tolerates terms that a skilled reader can pin down using the patent’s own teaching.

The procedural posture mattered. Because indefiniteness is a legal conclusion, the Federal Circuit reviewed it de novo, but it reviewed any subsidiary factual findings — for instance, what a person of ordinary skill would understand a term to mean — for clear error. And the burden runs against the challenger: any fact critical to an indefiniteness holding must be shown by clear and convincing evidence, the same heightened standard that governs invalidity generally. Those allocations frame why the district court’s approach was vulnerable on appeal.

The “enlarged chamber” and the intrinsic-record rule

The dispute over “enlarged chamber” was, at bottom, a fight about where to look. “Enlarged” is a classic term of degree — it presupposes a comparison, and a term of degree is indefinite only if the patent fails to supply some objective baseline against which the skilled artisan can measure it. The district court reasoned that the ‘877 patent never said what the enlarged chamber had to be larger than, and so concluded the term lacked objective boundaries. To fill the gap it consulted a dictionary definition of “enlarge.”

That was the error. The Federal Circuit held that the intrinsic record already told a skilled artisan what the term meant in the context of this invention. The ‘877 patent describes a viscometer whose defining innovation is a chamber large enough to hold excess test sample so that, when pressurization fluid compresses the sample, the sample level never falls below the transition point into the lower measurement zone — keeping the pressurization fluid out of the chamber where viscosity is measured and thereby eliminating the mixing errors that plagued prior-art designs. Read against that purpose, the panel explained, “enlarged chamber” denotes a chamber large enough to prevent pressurization fluid from entering the lower section where the sample’s viscosity is measured. The comparison the district court thought was missing was supplied by the specification’s account of the problem the chamber solves.

The methodological holding is the durable one. Where the intrinsic record — claims, specification, and prosecution history — resolves the meaning of a disputed term, “there is no reason to resort to extrinsic evidence,” and a court errs when it lets a general-purpose dictionary contradict the meaning the patentee gave a term. Extrinsic evidence such as a dictionary is a fallback, not a starting point, and it cannot override the patent’s own lexicography. Because the district court inverted that hierarchy, the panel vacated both the indefiniteness ruling and the invalidity determinations that rested on it, and remanded for further proceedings consistent with the proper reading of the term.

Means-plus-function under § 112(f)

The same opinion shows the other face of § 112. The sixth paragraph — § 112(f) — lets a patentee claim an element “as a means or step for performing a specified function” without reciting the supporting structure, but it exacts a price: the claim is construed to cover only the corresponding structure disclosed in the specification and its equivalents. A means-plus-function term that finds no corresponding structure in the specification is indefinite; one that does is simply confined to that structure.

The term “means for driving said rotor to rotate located in at least one bottom section” used the word “means” and indisputably invoked § 112(f). The work on appeal was identifying the corresponding structure and its location. The specification disclosed that the rotor could be driven by magnetic coupling or, as the patent put it, “driven to rotate with any means such as directly driven at the bottom of the cell body with dynamic seal.” The Federal Circuit agreed with the district court that the disclosed structure was therefore magnetic coupling or a direct drive at the bottom of the cell body, plus known equivalents. It rejected Grace’s attempt to redefine the “means for driving” as any single component that relays power to the rotor — the specification made clear that the magnetic-coupling components operate together, so no lone part could be the structure. It also rejected the argument that tying the structure to its location improperly read a limitation out of the written description into the claim; under § 112(f), the panel reasoned, the disclosed structure cannot be divorced from the location the patentee disclosed for it. The construction was affirmed.

Open questions

The remand leaves the ultimate fate of “enlarged chamber” unresolved. The Federal Circuit held only that the term is not indefinite on the present record and gave it meaning; it did not decide infringement, and it left room for further fact-finding consistent with its reading. Whether the claims survive on the merits remains for the district court. The opinion also does not purport to immunize every term of degree — it reaffirms that a term of degree still needs an objective anchor, and the holding is that this patent supplied one, not that comparison words are categorically safe.

Implications

  • Litigate the intrinsic record first. A definiteness challenge built on a dictionary is fragile when the specification explains the problem a term of degree solves; the objective baseline a court demands is often buried in the patent’s account of the prior art it improves on.
  • Terms of degree survive on purpose. Drafters can make “enlarged,” “substantial,” or similar words defensible by describing, in the specification, the function the feature performs and the failure mode it avoids — that functional context supplies the comparison a court needs.
  • Extrinsic evidence is a fallback. Courts and challengers cannot use a general dictionary to contradict a meaning the intrinsic record makes clear; the hierarchy of evidence is itself a rule of law that can be reversed on appeal.
  • “Means” still binds you to your structure — and its location. A means-plus-function term is only as broad as the structure the specification discloses, and Grace confirms that disclosed location can be part of that structure.
  • The same patent can win and lose under § 112. Definiteness and means-plus-function are distinct inquiries; a favorable ruling on one says nothing about the other.

Frequently asked questions

Did the Federal Circuit hold that “enlarged chamber” is definite? Not exactly. It held the term is not indefinite on this record and gave it a construction tied to the patent’s purpose, then vacated the contrary ruling and remanded. The district court can take up remaining issues consistent with that reading.

Why was it error to use a dictionary? Because the intrinsic record already resolved the term’s meaning. When the claims, specification, and prosecution history make a term’s scope reasonably certain, a court has no occasion to consult extrinsic evidence, and it cannot let a dictionary override the meaning the patentee supplied.

How can a vague-sounding term of degree be definite? A term of degree is definite when the patent provides an objective baseline for the comparison it implies. Here the specification explained that the chamber must be large enough to keep pressurization fluid out of the measurement zone — a functional benchmark a skilled reader could apply.

Authorities and sources