In Grace Instrument Industries, LLC v. Chandler Instruments Co., No. 2021-2370 (Fed. Cir. Jan. 12, 2023), the Court of Appeals for the Federal Circuit (“the Federal Circuit”) issued an opinion affirming in part, vacating in part, and remanding a decision of the United States District Court for the Southern District of Texas finding a first claim term indefinite, construing a second claim term, and holding all asserted claims of U.S. Patent No. 7,412,877 (the “’877 Patent”) invalid and/or not infringed.


Grace Instrument Industries, LLC (“Grace”) asserted claims 1, 2, 4, 5, 7-9, 11, 14, 15, and 17 of the ’877 Patent against Chandler Instruments Co., LLC (“Chandler”). Grace, No. 2021-2370 at 7. The ’877 Patent is directed to liquid-pressurized viscometers and similar devices used to measure the viscosities of samples of drilling fluids used in oil drilling apparatuses. Id. at 2-7. The ’877 Patent’s viscometer includes at least two separate chambers: (1) a lower measurement chamber that is completely filled with sample drilling fluid before and after pressurization, and (2) an additional chamber large enough to hold enough excess sample drilling fluid such that, when the sample is compressed, the point at which the sample and pressurization fluid meet remains in the additional chamber. Id. at 3-5.

The district court issued a claim construction order in which it (1) determined that the claim term “enlarged chamber” was indefinite, and (2) adopted Chandler’s construction for the claim term “means for driving said rotor to rotate located in at least one bottom section.” Id. at 7-9. Based on that claim construction order, the parties subsequently stipulated that claims 1, 2, 4, 5, 7-9, 11, 14, 15, and 17 were invalid and claims 4, 5, 7-9, 11, 14, 15, and 17 were not infringed. Id. at 9.

The two claim terms at issue — “enlarged chamber” and “means for driving said rotor to rotate located in at least one bottom section”—are found in claims 1 and 4 of the ’877 Patent, which read as follows:

1. A pressurized device comprising:

(a) a pressure vessel within which is vertically disposed at least one top section filled with a pressurization fluid of a first density and at least one lower section filled with a test sample of a second density,

(b) an enlarged chamber with reduced openings positioned between the at least one top section and the at least one bottom section for communicating pressure with said top section and said lower section within said pressure vessel,

(c) whereby said pressurization fluid would not mix with said test sample because of the nature of their density difference.

4. Viscometer comprising:

(a) a pressure vessel within which at least one top section filled with a pressurization fluid of a first density,

(b) within said pressure vessel a rotor which is driven to rotate while contacting with a sample liquid of a second density to be measured,

(c) means for driving said rotor to rotate located in at least one bottom section,

(d) a bob within said rotor,

(e) an enlarged chamber with reduced openings positioned between the at least one top section and the at least one bottom section for communicating pressure located above said bob,

(f) whereby said pressurization fluid would not mix with said sample liquid because of the nature of their density difference.

’877 Patent at 12:34-47, 12:52-67 (emphases added); Grace, No. 2021-2370 at 6-7.

The district court determined that the adjective “enlarged” “is a ‘term of degree’ that ‘necessarily calls for some comparison” of the size of the “enlarged chamber” “against some baseline.’” Id. at 7 (quoting Grace Instrument Indus., LLC v. Chandler Instruments Co., No. 4:20-cv-1749, 2021 WL 2711987, at *5 (S.D. Tex. July 1, 2021)). However, according to the district court, the ’877 Patent failed to provide such a baseline or other “‘objective boundaries’ for a skilled artisan” to use in determining just how large the “enlarged chamber” needed to be. Id. (quoting Grace, 2021 WL 2711987, at *5). Relying on Liberty Ammunition, Inc. v. United States, 835 F.3d 1388 (Fed. Cir. 2016), the district court concluded that the term “enlarged chamber” was indefinite. Id. In reaching this conclusion, the district court rejected Grace’s assertions that (1) the meaning of “enlarged chamber” could be ascertained solely based on the chamber’s purpose and/or function; and (2) that the appropriate point of comparison for the modifier “enlarged” was the prior art, as this was “not evident from the ’877 Patent itself.” Id. (quoting Grace, 2021 WL 2711987, at *5).

With regard to the second claim term, “means for driving said rotor to rotate located in at least one bottom section,” the parties agreed that such term was a means-plus-function term under 35 U.S.C. § 112, ¶ 6. The district court subsequently conducted an extensive claim construction analysis and concluded that the function of the limitation was “driving said rotor to rotate, where the means for driving is located in at least one bottom section” and that the corresponding structure was a “(i) magnetic coupling . . . , or (ii) direct drive at bottom of cell body, and known equivalents.” Id. at 7-9.

The Federal Circuit’s Analysis and Conclusion

The Federal Circuit began its review of the district court’s indefiniteness ruling by emphasizing the general rule that claim construction analyses should begin and end with the intrinsic evidence of record (i.e., the specification, claims, and prosecution history) “[i]f the meaning of a claim term is clear from the intrinsic evidence.” Id. at 10 (quoting Seabed Geosols. (US) Inc. v. Magseis FF LLC, 8 F.4th 1285, 1287 (Fed. Cir. 2021)). Turning to the intrinsic record, then, the Federal Circuit determined that such record clearly informed a skilled artisan as to the size of the “enlarged chamber.” Specifically, the court explained that the “enlarged chamber” must be:

[L]arge enough to prevent pressurization fluid from entering the lower section of the pressure vessel—where the viscosity of the test sample is being measured—during elevated pressurization. In other words, the enlarged chamber has to be able to contain enough sample fluid at the pre-pressurization stage such that, during pressurization, the sample fluid level does not fall below the bottom of the enlarged chamber and into the viscometer’s lower, testing section. This design ensures that any mixing of the pressurization fluid and compressed sample fluid occurs within the enlarged chamber and not in the lower, testing section.

Id. at 11. Thus, contrary to the district court’s conclusion, what was determinative of the meaning of the comparative adjective “enlarged” in the claim term “enlarged chamber” was not the size of “some baseline object,” but rather the function that the chamber was designed to accomplish. Id.

According to the Federal Circuit, this meaning would be evident from both the specification and the prosecution history, because each highlighted how the claimed invention was designed to eliminate measurement errors that plagued prior art viscometers that relied on either (1) density differences between drilling fluids and pressurization fluids, or (2) physical seals designed to isolate the drilling fluid samples to ensure that the viscosities of only the drilling fluid samples were measured. Id. at 11-13. Notably, the intrinsic record emphasized that the invention purportedly eliminated these measurement errors by incorporating the “enlarged chamber.” Id. This “enlarged chamber” could be filled with enough sample drilling fluid to allow it to completely contain the interface between the sample and pressurization fluid and ensure that no pressurization fluid mixed with the sample in the lower measurement chamber when the pressurization fluid was added to compress the sample. Id. at 12-13. Accordingly, the Federal Circuit concluded that, even though the term “enlarged chamber” is not a term of art, “the intrinsic record sufficiently guides a skilled artisan to the meaning of that term as used in the ’877 patent.” Id. at 13. This, the Federal Circuit explained, was true even though the term “enlarged chamber” appeared only twice in the specification and even though the specification contained no explicit definition for the term. Id. at 13-14.

The Federal Circuit rejected as erroneous the district court’s use of dictionary definitions to conclude that the term “enlarged” could only be defined by reference to some other object, noting that such “extrinsic evidence . . . contradict[ed] the scope and meaning of ‘enlarged chamber’ that a skilled artisan would ascertain by reading the intrinsic record.” Id. at 13. The Federal Circuit indicated that such use violated the general principle that “[a] court . . . may rely on dictionary definitions[] ’so long as the dictionary definition[s] do[] not contradict any definition found in or ascertained by a reading of the patent documents.” Id. at 10 (quoting Phillips v. AWH Corp., 415 F.3d 1303, 1317, 1322-23 (Fed. Cir. 2005) (en banc)).

Attributing the district court’s error to its reliance on Liberty Ammunition, the Federal Circuit went on to distinguish that case from the case at bar. Id. at 14. The Federal Circuit explained that, whereas the claim term at issue in Liberty Ammunition had to be “compared to the [prior art] because there was no other objective boundary for a skilled artisan,” “[h]ere . . . the intrinsic record provide[d] an objective boundary” by stressing that the “enlarged chamber” must be large enough to accomplish its intended function. Id. In this way, the instant case analogized much more closely to the facts in Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 898, 901 (2014) and the “reasonable certainty” standard it set forth.

In view of the above, the Federal Circuit construed “enlarged chamber” to mean “a chamber that is large enough to contain excess test sample prior to pressurization to prevent mixing of the test sample and pressurization fluid in the lower measurement zone when the test sample is pressurized to a maximum rated pressure.” Id. at 16. However, the Federal Circuit acknowledged that there were still outstanding factual issues relating to the district court’s indefiniteness ruling that would be more properly addressed on remand. Id. at 15-16. It accordingly vacated and remanded the district court’s indefiniteness determination and invalidity determinations based thereon. Id. at 16-17.

Separately, the Federal Circuit agreed with the district court’s means-plus-function construction and affirmed the court’s noninfringement determinations. Id. at 17-22.


With this opinion, the Federal Circuit simultaneously (and somewhat paradoxically) underscored both the rigidity and fluidity of claim construction analyses. On one hand, the Court stressed the fundamental principles that any such analysis should be conducted in a stepwise fashion, beginning with the intrinsic evidence and considering any extrinsic evidence only when (1) the intrinsic evidence leaves the meaning of a claim term ambiguous; and (2) the extrinsic evidence does not contradict the clear import of the intrinsic evidence. On the other hand, however, the Court clearly indicated that a decision-maker engaging in claim construction must approach intrinsic evidence with a significant amount of analytical flexibility.

Specifically, when examining a claim term incorporating a comparative adjective or other word of degree, the standard of “reasonable certainty” to one of ordinary skill in the art may be met when the intrinsic record provides sufficient parameters or “objective boundaries” for a skilled artisan to make the comparison based on functional terms rather than a baseline comparison.

This case may cause some to wonder how much interpretive and exegetical gymnastics are appropriate to save patents. For practitioners, an ounce of prevention in drafting the specification may be worth many, many pounds of cure. The challenge is to spot relative terms in a draft specification. If such terms are not defined in the specification, in an abundance of caution, the practitioner can develop and include in the specification a definition for the term. The Nautilus standard of “reasonable certainty” to one of ordinary skill in the art is the claim drafting objective to keep in front of mind.

†Stacy Lewis is a Law Clerk at Finnegan.