United States Court of Appeals 

for the Federal Circuit ______________________ 

GRACE INSTRUMENT INDUSTRIES, LLC,

Plaintiff-Appellant

v.

CHANDLER INSTRUMENTS COMPANY, LLC, 

AMETEK, INC.,

Defendants-Appellees

______________________ 

2021-2370

______________________ 

Appeal from the United States District Court for the 

Southern District of Texas in No. 4:20-cv-01749, Judge Andrew S. Hanen.

______________________ 

Decided: January 12, 2023

______________________ 

BRADFORD TURNER LANEY, Raley & Bowick, LLP, Houston, TX, argued for plaintiff-appellant. Also represented 

by ROBERT MCGEE BOWICK, JR. 

 JULIE S. GOLDEMBERG, Morgan, Lewis & Bockius LLP, 

Philadelphia, PA, argued for defendants-appellees. Also 

represented by EUGENE HWANGBO, JASON C. WHITE, Chicago, IL; ARCHIS VASANT OZARKAR, WILLIAM R. PETERSON,

MELISSA MARIE STORY, Houston, TX. 

 ______________________ 

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Before CHEN, CUNNINGHAM, and STARK, Circuit Judges.

CHEN, Circuit Judge. 

Grace Instrument Industries, LLC (Grace) appeals a 

claim construction order issued by the United States District Court for the Southern District of Texas finding the 

term “enlarged chamber” indefinite and construing the 

term “means for driving said rotor to rotate located in at 

least one bottom section.” As a result of the district court’s 

order, the parties stipulated that asserted claims 1, 2, 4, 5, 

7–9, 11, 14, 15, and 17 of U.S. Patent No. 7,412,877 

(’877 patent) are invalid and that claims 4, 5, 7–9, 11, 14, 

15, and 17 are not infringed, and the court entered final 

judgment in favor of Chandler Instruments Company, LLC 

(Chandler). Because the district court erred in its analysis 

of the term “enlarged chamber,” we vacate the district 

court’s determination that “enlarged chamber” is indefinite

and remand for further proceedings consistent with this 

opinion. We affirm the district court’s construction of 

“means for driving said rotor to rotate located in at least 

one bottom section.” 

BACKGROUND

I 

When drilling oil wells, drilling fluid is used to drive a 

drill bit and bring drill cuttings back to the surface of the 

well. ’877 patent col. 1 ll. 17–19. The drilling fluid’s viscosity is critical to the well’s operation—too high and the 

fluid is too hard to pump; too low and the fluid cannot carry 

the drill cuttings back to the surface. Id. at col. 1 ll. 19–24. 

Thus, before use, drilling fluid viscosity is first measured 

using a viscometer that simulates “down-hole” conditions—

i.e., the temperature and pressure at the drill bit while 

drilling. Id. at col. 1 ll. 26–28. 

In a liquid pressurized viscometer, pressurization fluid

is added to pressurize the sample drilling fluid within the 

viscometer to down-hole conditions while the sample fluid 

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is stirred by a rotor to measure its viscosity. The introduction of the pressurization fluid compresses the sample drilling fluid, causing it to take up less volume within the 

viscometer. Ideally, the pressurization fluid does not mix 

with the sample fluid being measured to ensure that the 

viscometer reports the viscosity of only the sample fluid

and not the viscosity of a mixture of the two fluids. Id. at 

col. 1 ll. 53–56, col 5 ll. 55–57, col. 5 ll. 59–62, col. 12 

ll. 21–23. 

Before the ’877 patent, liquid pressurized viscometers

separated the sample fluid from the pressurization fluid in 

one of two ways. Some viscometers relied on the density 

difference between the fluids, but if some pressurization 

fluid entered the chamber where the sample fluid was being tested, stirring by the rotor would cause the two fluids 

to mix, leading to measurement errors. Id. at col. 1 

ll. 53–56, col. 5 ll. 59–62. Other viscometers used a seal to 

separate the two fluids, but friction caused by the sample 

fluid rubbing against the seal as the sample fluid was 

stirred led to inaccurate results. Id. at col. 1 ll. 43–46, col. 5 

ll. 57–59. 

The ’877 patent’s viscometer purportedly eliminates 

measurement errors caused by seal friction or commingling 

of sample and pressurization fluids by offering a different 

solution. Id. at col. 2 ll. 1–3, col. 12 ll. 21–23. Instead of 

using a seal to separate the fluids, the ’877 patent’s viscometer includes an “enlarged” chamber located between a 

lower chamber, housing the sample fluid, and a pressurization fluid inlet, located in the top section of the viscometer’s pressure vessel. This enlarged chamber is large 

enough such that the level of the sample fluid, which before 

pressurization initially fills both the lower chamber and 

the enlarged chamber, never falls below the transition 

point between the lower chamber and enlarged chamber 

when the application of the pressurization fluid compresses 

the sample fluid. By keeping the sample fluid level above 

the top of the lower chamber and within the enlarged 

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chamber, even when the sample fluid is compressed, the 

claimed viscometer design ensures that any mixing between the two fluids occurs within the enlarged chamber 

and no pressurization fluid enters the lower chamber

where the sample fluid is being tested. Id. at col. 5 l. 55 – 

col. 6 l. 6; see also id. at col. 8 ll. 37–48, col. 10 ll. 49–60. 

Thus, the ’877 patent’s design is intended to “[t]otally eliminate the measurement error because of sample mixing 

with pressurization fluid in a comparative viscometer.” Id. 

at col. 12 ll. 21–23.

The ’877 patent discloses three embodiments of its viscometer. The first embodiment is shown below.

Id. FIG. 1 (exploding out chambers 45 and 49); see also id. 

FIG. 2, FIG. 3. In each embodiment, chambers 45 and 49 

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act together to contain the pressurization fluid as the sample fluid in a “lower measurement zone” is compressed: 

[W]hen pressurization fluid is applied, the sample 

fluid level is pushed down due to the compressibility of tested sample. Thus initial sample fluid inside of chamber 45 goes down to chamber 49 

through small gap 25, and some of the initial sample fluid inside of chamber 49 goes down to the 

lower measurement zone through small gap 27. 

However, chamber 45 and chamber 49 are large 

enough so that at maximum rated pressure, chamber 49 is still at least half filled with sample fluid. 

This ensures the accuracy of the measurement because measurement zone below anti mixer bottom 

fin 82 is always totally filled with sample fluid.

Id. at col. 5 l. 63 – col. 6 l. 6; see also id. at col. 8 ll. 37–48, 

col. 10 ll. 49–60. Although the three embodiments use both 

chamber 45 and chamber 49, the ’877 patent also explains 

that “[i]t is not necessary to have both chamber 45 and 

chamber 49.” Id. at col. 10 ll. 64–65. “With just chamber 45 or chamber 49 and sufficient volume, pressurization fluid and test sample can still be separated well.” Id. 

at col. 10 ll. 65–67 (emphasis added). 

To measure the viscosity of the sample fluid in the 

lower measurement zone, the ’877 patent discloses a rotor 

that is driven by magnetic coupling but also “could be 

driven to rotate with any means such as directly driven at 

the bottom of the cell body with dynamic seal, etc.” Id. at

col. 2 ll. 11–13, col. 4 ll. 54–59, col. 5 ll. 42–54, col. 7 

ll. 41–47, col. 8 ll. 24–36, col. 9 ll. 61–67, col. 10 ll. 36–48, 

col. 11 ll. 41–43.

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Claims 1 and 4 are independent claims that claim a 

pressurized device and a viscometer, respectively: 

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,

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(f) whereby said pressurization fluid would 

not mix with said sample liquid because of 

the nature of their density difference.

Id. at col. 12 ll. 34–47, col. 12 ll. 52–67 (emphases added). 

The two italicized claim terms are the focus of this appeal. 

II

On May 19, 2020, Grace sued Chandler in the United 

States District Court for the Southern District of Texas, alleging that Chandler’s Model 7600 viscometer infringed

multiple claims of the ’877 patent. J.A. 52; J.A. 61–65. On 

July 1, 2021, the district court issued its claim construction 

order. Grace Instrument Indus., LLC v. Chandler Instruments Co., No. 4:20-cv-1749, 2021 WL 2711987 (S.D. Tex. 

July 1, 2021) (Claim Construction Order). 

Relevant here, the district court held that the term “enlarged chamber” in claims 1 and 4 is indefinite. Id. at *4–5. 

The district court explained that “enlarged” is a “term of 

degree” that “necessarily calls for some comparison against 

some baseline.” Id. at *5 (quoting Liberty Ammunition, 

Inc. v. United States, 835 F.3d 1388, 1395 (Fed. Cir. 2016)). 

Finding that the ’877 patent “does not provide the requisite 

objective boundaries” for a skilled artisan, the district court 

held that “enlarged chamber” is indefinite. Id. at *5. The 

district court rejected Grace’s argument that “enlarged 

chamber” could be defined by its purpose, finding that “explaining that something is large enough to do a certain task 

does not answer the question: larger than what?” Id. The

district court further disagreed with Grace that the baseline for “enlarged” is the prior art, explaining that “this is 

not evident from the ’877 Patent itself.” Id.

The district court also construed “means for driving 

said rotor to rotate located in at least one bottom section.” 

Id. at *7–8. The parties agreed that the term was subject 

to 35 U.S.C. § 112, ¶ 6 (pre-AIA), and the table below illustrates the parties’ positions on the construction: 

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Id. at *7; J.A. 34. The parties thus agreed that the function 

is “driving said rotor to rotate,” but they disputed the 

means and whether the phrase “located in at least one bottom section” modifies “rotor,” as Grace contended, or 

“means for driving,” as Chandler argued. Claim Construction Order, 2021 WL 2711987, at *7. 

To resolve the dispute, the district court looked to 

claim 14, which depends from claim 4 and recites:

14. The viscometer of claim 4 wherein said means 

for driving said rotor to rotate is a magnetic coupling across said pressure vessel wall. 

’877 patent col. 13 ll. 22–24. The district court found that 

Grace’s proposed construction of the means (1) was “not 

broad enough to include magnetic coupling” as it must because of dependent claim 14 and (2) would exclude other 

terms described in the patent as causing the rotor to rotate. 

Claim Construction Order, 2021 WL 2711987, at *7 (citing 

’877 patent col. 5 ll. 45–47 (magnet mount), col. 4 ll. 55–59 

(gear box, motor, driving magnet, or coupling magnet), 

col. 12 ll. 41–43 (direct drive at bottom of the cell body)). 

Thus, the district court adopted Chandler’s proposed construction of the means. 

The district court also agreed with Chandler that “located in at least one bottom section” modifies “means for 

driving,” not “rotor.” Id. at *8. The district court explained 

that this interpretation “conform[s] with [the] usual rules 

of grammar and sentence structure” and is confirmed by 

limitation 4(b), which already describes the rotor’s location 

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as “within said pressure vessel,” not necessarily in the “bottom section.” Id. 

Thus, the district court adopted in its entirety Chandler’s proposed construction of “means for driving said rotor to rotate located in at least one bottom section.” Id. 

Accordingly, the function of the “means for driving” limitation is “driving said rotor to rotate, where the means for 

driving is located in at least one bottom section,” and the 

corresponding structure is “(i) magnetic coupling (magnetic 

mount, gear box or motor, driving magnet, coupling magnet), or (ii) direct drive at bottom of cell body, and known 

equivalents.” Id. at *7–8.

The parties then stipulated that claims 1, 2, 4, 5, 7–9, 

11, 14, 15, and 17 are invalid based on the district court’s 

determination that “enlarged chamber” is indefinite, and 

that claims 4, 5, 7–9, 11, 14, 15, and 17 are not infringed 

based on the district court’s construction of “means for driving said rotor to rotate in at least one bottom section.” 

J.A. 1529–34. The district court entered a final judgment 

on September 23, 2021. J.A. 19–20. 

Grace timely appealed. We have jurisdiction under 28 

U.S.C. §§ 1291 and 1295(a)(1). 

DISCUSSION

Claim construction requires determining how a skilled 

artisan would understand a claim term “in the context of 

the entire patent, including the specification.” Phillips v. 

AWH Corp., 415 F.3d 1303, 1313 (Fed. Cir. 2005) (en banc). 

We begin by considering the language of the claims themselves. Id. at 1314. However, “claims must be read in view 

of the specification, of which they are a part.” Id. at 1315 

(internal quotation marks omitted) (quoting Markman v. 

Westview Instruments, Inc., 52 F.3d 967, 978 (Fed. Cir. 

1995) (en banc)). We have explained that the specification 

is the “single best guide to the meaning of a disputed term,” 

Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582 

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(Fed. Cir. 1996), and “is, thus, the primary basis for construing the claims,” Phillips, 415 F.3d at 1315 (citation and 

internal quotation marks omitted). A court also should 

consider the patent’s prosecution history, and may rely on 

dictionary definitions, “so long as the dictionary definition 

does not contradict any definition found in or ascertained 

by a reading of the patent documents.” Id. at 1317, 

1322–23 (citation and internal quotation marks omitted).

We review claim construction based on intrinsic evidence de novo and review any findings of fact regarding extrinsic evidence for clear error. SpeedTrack, Inc. v. 

Amazon.com, Inc., 998 F.3d 1373, 1378 (Fed. Cir. 2021) (citing Teva Pharms. USA, Inc. v. Sandoz, Inc., 574 U.S. 318,

331–32 (2015)). Intrinsic evidence includes the patent’s 

claims, specification, and prosecution history. Cont’l Cirs. 

LLC v. Intel Corp., 915 F.3d 788, 795 (Fed. Cir. 2019). Extrinsic evidence is “secondary to the intrinsic evidence” and 

“consists of all evidence external to the patent and prosecution history, including expert and inventor testimony, 

dictionaries, and learned treatises.” Id. at 799 (quoting

Phillips, 415 F.3d at 1317). “If the meaning of a claim term 

is clear from the intrinsic evidence, there is no reason to 

resort to extrinsic evidence.” Seabed Geosolutions (US) Inc. 

v. Magseis FF LLC, 8 F.4th 1285, 1287 (Fed. Cir. 2021).

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.” Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 

898, 901 (2014). “The ultimate conclusion that a claim is 

indefinite under 35 U.S.C. § 112, ¶ 2 is a legal conclusion, 

which we review de novo.” Cox Commc’ns, Inc. v. Sprint 

Commc’n Co., 838 F.3d 1224, 1228 (Fed. Cir. 2016) (citation 

omitted). “As in claim construction, we review a district 

court’s underlying factual determinations for clear error.” 

Id. (citations omitted). Moreover, “[a]ny fact critical to a 

holding on indefiniteness . . . must be proven by the 

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challenger by clear and convincing evidence.” Id. (alteration in original) (citation and internal quotation marks 

omitted).

I. Enlarged Chamber

Grace argued before the district court that the term 

“enlarged chamber” should be construed as “the area between reduced openings that is large enough to hold excess 

test sample (i.e., the type of fluid normally used in these 

machines) to prevent mixing of pressurization fluid and 

test sample below the bottom fin during elevated pressurization.” Claim Construction Order, 2021 WL 2711987, 

at *5. The district court declined to adopt that construction, concluding that the ’877 patent fails to disclose objective boundaries for a skilled artisan to know what the 

claimed “enlarged chamber” must be larger than. Id. This 

was error. The intrinsic record informs a skilled artisan

that the ’877 patent and its claims are directed to a viscometer with an “enlarged chamber” that is large 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. Thus, in the 

context of this patent, “enlarged chamber” does not require 

that chamber to be larger than some baseline object; rather 

it must be large enough to accomplish a particular function. 

The ’877 patent’s specification guides us to the term’s 

meaning. The specification explains that “[o]ne of the 

drawbacks of most liquid pressurized viscometers is the 

mixing between tested sample and pressurization fluid,” 

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which leads to inaccurate test results. ’877 patent col. 5 

ll. 55–57, col. 5 ll. 59–62; see also id. at col. 1 ll. 53–56. According to the patent, prior art viscometers attempted to 

remedy this inaccuracy by using a seal between the pressurization fluid and sample fluid, but the seal “induce[s] 

friction error causing inaccurate measurement.” Id. at 

col. 5 ll. 57–59; see also id. at col. 1 ll. 43–46; discussion supra Background § I. The ’877 patent explains that the “current invention” solves this problem through use of 

chambers 45 and 49: “[C]hamber 45 and chamber 49 are 

large enough so that at maximum rated pressure, chamber 

49 is still at least half filled with sample fluid. This ensures 

the accuracy of the measurement because measurement zone 

below anti mixer bottom fin 82 is always totally filled with 

sample fluid.” ’877 patent col. 6 ll. 2–6 (emphases added). 

The patent discloses the same for two other embodiments, 

id. at col. 8 ll. 43–48, col. 10 ll. 55–60, and explains that a 

single chamber could be used instead of two chambers (i.e., 

chamber 45 and chamber 49), provided the single chamber

has “sufficient volume,” id. at col. 10 ll. 64–67. Finally, the 

specification explains that “[b]y providing an enlarged 

chamber such as chamber 45 or chamber 49 . . . this configuration can be applied to other applications than viscometers to reduc[e] the mixing of test sample and 

pressurization fluid.” Id. at col. 11 ll. 28–32 (emphasis 

added). A skilled artisan would understand from these disclosures that the “enlarged chamber” comprises chambers 45 and/or 49 and is large enough to prevent the 

pressurization fluid from mixing with the sample fluid in 

the lower measurement zone during elevated pressurization, thus avoiding measurement errors caused by commingling of the sample and pressurization fluids in prior-art 

viscometers. 

The prosecution history supports this understanding. 

In response to a rejection over U.S. Patent No. 4,633,708 

(Blommaert), which taught use of a seal, the applicant explained “[b]y having ‘an enlarged chamber with reduced 

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openings for communicating pressure’, pressurization oil 

will not contaminate [the] test sample even without a seal 

as described in Blommaert.” J.A. 1063; see also 

J.A. 1066–67, 1069–70. The applicant also explained that 

the “[c]urrent invention solved a long lasting problem” in 

high-pressure testing of drilling fluids, including “the large 

measurement error . . . induced due to the friction of the 

seal” in designs like Blommaert. J.A. 1062–63; see also 

J.A. 1064, 1066, 1068, 1070. The examiner subsequently 

allowed the claims. A skilled artisan would understand 

from the prosecution history that the purpose and role of 

the ’877 patent’s “enlarged chamber” is to prevent commingling of the sample and pressurization fluids in the lower 

measurement zone without using a seal, thereby avoiding 

the measurement errors seen in prior-art viscometers like

Blommaert. 

Thus, although “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. The 

district court erred in its reliance on extrinsic evidence—

i.e., dictionary definitions—that contradict the scope and 

meaning of “enlarged chamber” that a skilled artisan 

would ascertain by reading the intrinsic record. See Phillips, 415 F.3d at 1322–23; see also id. at 1316 (“[O]ur cases 

recognize that the specification may reveal a special definition given to a claim term by the patentee that differs from 

the meaning it would otherwise possess.”); Trs. of Columbia Univ. v. Symantec Corp., 811 F.3d 1359, 1363 (Fed. Cir. 

2016) (“The only meaning that matters in claim construction is the meaning in the context of the patent.”). Where 

the specification instructs as to the meaning of a claim 

term, “the inventor’s lexicography governs.” Phillips, 415 

F.3d at 1316. 

Chandler, for its part, is correct that the ’877 patent’s 

specification refers to “enlarged chamber” only twice, but, 

for the reasons already stated, a skilled artisan would understand that the specification’s descriptions of an 

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enlarged chamber and the corresponding embodiments adequately guide the skilled artisan to the meaning of “enlarged chamber.” Further, to the extent Chandler would 

require an explicit definition of the term “enlarged chamber,” that is incorrect. As our en banc opinion in Phillips

explained, a “claim term may be clearly redefined without 

an explicit statement of redefinition,” and “[e]ven when 

guidance is not provided in explicit definitional format, the 

specification may define claim terms by implication such 

that the meaning may be found in or ascertained by a reading of the patent documents.” 415 F.3d at 1320–21 (first 

quoting Bell Atl. Network Servs., Inc. v. Covad Commc’ns 

Grp., Inc., 262 F.3d 1258, 1268 (Fed. Cir. 2001); and then 

quoting Irdeto Access, Inc. v. Echostar Satellite Corp., 383 

F.3d 1295, 1300 (Fed. Cir. 2004)); see also Aventis Pharma 

S.A. v. Hospira, Inc., 675 F.3d 1324, 1330 (Fed. Cir. 2012) 

(“This clear expression need not be in haec verba but may 

be inferred from clear limiting descriptions of the invention 

in the specification or prosecution history.”). 

The district court’s reliance on dictionary definitions of 

“enlarged” rather than the meaning a skilled artisan would 

reasonably understand from the intrinsic record led, in 

part, to its reliance on Liberty Ammunition. There, we 

found that “reduced area of contact” must be compared to

the prior-art ammunition because there was no other objective boundary for a skilled artisan. Liberty Ammunition, 

835 F.3d at 1396–97 (citing Interval Licensing LLC v. AOL, 

Inc., 766 F.3d 1364, 1370–71 (Fed. Cir. 2014)). Here, however, the intrinsic record provides an objective boundary 

for a skilled artisan—i.e., the “enlarged chamber” must be 

large enough to prevent, during elevated pressurization,

commingling of sample and pressurization fluids in the 

lower measurement zone. Unlike Liberty Ammunition,

this objective boundary does not require a comparison to 

the size of prior-art chambers. 

Our decision in Biosig Instruments, Inc. v. Nautilus, 

Inc., 783 F.3d 1374 (Fed. Cir. 2015), is more applicable. 

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There, we reviewed claims directed to a heart rate monitor 

with a “spaced relationship” between a first live electrode 

and a first common electrode. Id. at 1376. We explained 

that, although the patent “does not specifically define 

‘spaced relationship’ with actual parameters,” the intrinsic 

evidence demonstrated that a “skilled artisan would be 

able to determine this language requires the spaced relationship to be neither infinitesimally small nor greater 

than the user’s hands”: 

For example, on the one hand, the distance between the live electrode and the common electrode 

cannot be greater than the width of a user’s hands 

because claim 1 requires the live and common electrodes to independently detect electrical signals at 

two distinct points of a hand. On the other hand, 

it is not feasible that the distance between the live 

and common electrodes be infinitesimally small, effectively merging the live and common electrodes 

into a single electrode with one detection point.

Id. at 1382–83 (quoting Biosig Instruments, Inc. v. Nautilus, Inc., 715 F.3d 891, 899 (Fed. Cir. 2013), vacated sub 

nom. Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 

898 (2014)). Thus, we found that “a skilled artisan would 

understand the inherent parameters of the invention as

provided in the intrinsic evidence.” Id. at 1384. The same 

is true here. A skilled artisan would understand the inherent parameters of the “enlarged chamber” through the intrinsic evidence. Like the spaced relationship in Nautilus, 

the “enlarged chamber” must be a certain minimum size, 

or large enough, to maintain sample fluid within the enlarged chamber when the sample fluid is under elevated 

pressurization.

Although we disagree with the district court’s conclusion that “enlarged chamber” must be larger than something else rather than large enough to achieve a particular 

purpose, it appears that the indefiniteness question is not 

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yet fully resolved and may require further fact finding on 

remand. Chandler, for example, argues that the term “enlarged chamber” is still indefinite because the claims recite 

an additional limitation that relies on the “density difference” between the fluids—not the enlarged chamber—to 

prevent mixing. Appellee’s Br. 20–22, 32–33. Chandler 

also argues that different sample fluids will compress in 

different amounts under the same pressure, and thus a 

skilled artisan cannot determine if a given viscometer’s 

chamber satisfies the “enlarged chamber” limitation due to 

the variance in how much different sample fluids compress. 

Appellee’s Br. 23–25, 32–33; see also Appellee’s Letter, 

Aug. 8, 2022, ECF No. 50. Grace disagrees with the merits 

of both arguments and asserts that both arguments are 

waived because they were not raised before the district 

court. Appellant’s Reply Br. 4–7, 15–19; Appellant’s Letter, Aug. 11, 2022, ECF No. 53. Grace also makes additional arguments based on the extrinsic record. 

Appellant’s Br. 45–54. We will not address these arguments in the first instance. It is appropriate for the district 

court to consider these types of arguments on remand, including whether any have been waived. We also note that 

the district court made no finding as to the identity of the 

pertinent person of ordinary skill in the art, from whose 

perspective the “reasonable certainty” analysis must be undertaken. This oversight may well be due to the parties’ 

relative inattention to this factual issue, although the resolution of it may also be informative as to whether, on remand, the claims are again determined to be indefinite. 

See generally Nautilus, 572 U.S. at 901.

In sum, we find the term “enlarged chamber” in the 

’877 patent 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 maximum rated pressure.” We thus vacate the district court’s determination that “enlarged chamber” is 

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indefinite, vacate the district court’s invalidity determinations based thereon, and remand for further proceedings 

consistent with this opinion. 

II. Means for Driving Said Rotor to Rotate Located in 

at Least One Bottom Section

Grace also contests the district court’s construction of 

“means for driving said rotor to rotate located in at least 

one bottom section.” Grace argues that the court erred in 

finding that the term “bottom section” refers to the bottom 

section of the viscometer rather than the bottom section of 

the pressure vessel and in finding that “located in at least 

one bottom section” modifies “means for driving” rather 

than “rotor.” Appellant’s Br. 57–68, 70–71. According to 

Grace, the correct construction of “means for driving” includes a “magnet holder” and a “direct drive” that attaches 

to the bottom section of the rotor rather than “at bottom of 

cell body.” Appellant’s Br. 67–69. We disagree and thus 

affirm the district court’s construction. 

A. The District Court’s Construction

We first consider whether the phrase “located in at 

least one bottom section” in limitation 4(c) modifies “means 

for driving” or “rotor.” Starting with the claim language, 

we agree with the district court that the most natural reading of limitation 4(c) requires the phrase “located in at least 

one bottom section” to modify “means for driving” and not 

“rotor.” In this limitation, “means” is a noun modified by 

the prepositional phrase “for driving said rotor to rotate.” 

The noun “means” also is modified by the participle phrase

“located in at least one bottom section.” Because the prepositional phrase is unnecessary, the sentence is best read 

as a “means” that is “located in at least one bottom section.” 

Had the patentee intended for “located in at least one bottom section” to modify “rotor,” the patentee would have 

placed the “located in at least one bottom section” phrase 

before “to rotate.”

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That “means for driving said rotor to rotate” should be 

read as a unit, composed of a noun modified by a prepositional phrase, is confirmed by dependent claim 14. 

Claim 14 recites the viscometer of claim 4 “where said 

means for driving said rotor to rotate is . . . .” ’877 patent 

col. 13 ll. 23–24 (emphasis added). Thus, in claim 14, the 

same noun modified by the same prepositional phrase is 

used in the same manner as in claim 4, indicating that the 

patentee intended the noun and prepositional phrase to be 

read together. Thus, “located in at least one bottom section” modifies the entire “means” unit and not the “rotor.”

Comparing limitations 4(b) and 4(c) supports this interpretation. Limitation 4(b) introduces the “rotor” and explains that the rotor is located “within said pressure 

vessel.” Id. at col. 12 ll. 55–57. Limitation 4(c) introduces 

the “means for driving” and explains that the “means for 

driving” is “located in at least one bottom section.” Id. at 

col. 12 ll. 58–59. A skilled artisan reading claim 4 would 

understand that these limitations are directed to different 

components of the viscometer and also describe the corresponding locations for those components. Indeed, it would 

make little sense for limitation 4(b) to introduce the rotor, 

explain that it is located in the pressure vessel, and then, 

in a separate limitation directed to the “means for driving,” 

explain that the rotor is located in the bottom section. 

Next, we agree with the district court that the intrinsic 

record requires that the claimed “bottom section” refers to 

the bottom section of claim 4’s viscometer, not the pressure 

vessel component of the viscometer. Dependent claim 14 

explains that the “means for driving” is a “magnetic coupling across said pressure vessel wall.” Id. at col. 13 

ll. 23–25 (emphasis added). The “means for driving” thus 

cannot be in the bottom section of the pressure vessel because claim 14 requires the “means for driving” to operate 

across the pressure vessel wall—i.e., magnetic coupling 

components must be located inside and outside the pressure vessel. Thus, the “means for driving” must be in the 

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“bottom section” of the overall viscometer rather than the 

pressure vessel because that understanding encompasses 

the “means for driving” components located outside the 

pressure vessel. 

The structure of claim 4 is consistent with this interpretation. Claim 4 is directed to a “Viscometer.” Id. at

col. 12 l. 52. Limitations 4(a) and 4(b), however, are specifically tailored to aspects of the pressure vessel within the 

viscometer, whereas limitation 4(c) does not refer to the 

“pressure vessel.” Id. at col. 12 ll. 58–59. Reading these 

limitations together, a skilled artisan would interpret limitations 4(a) and 4(b) to refer to the pressure vessel and 

limitation 4(c) to refer to the “bottom section” the viscometer. 

This reading also is consistent with the specification, 

which explains that the primary “means for driving” the 

rotor is magnetic coupling: “A motor or gearbox drives 

magnet mount 40 to rotate carrying driving magnet 38 . . . . Due to the magnetic coupling between driving 

magnet 38 and coupling magnet 34, rotor 51 rotates at the 

same revolving speed as magnet mount 40 does.” Id. at

col. 5 ll. 42–47; see also id. at col. 8 ll. 24–30, col. 10 

ll. 36–42. The motor or gearbox, magnet mount 40, and 

driving magnet 38 are located outside the pressure vessel. 

See id. at FIGS. 1–3, col. 3 ll. 7–10. Because some of these 

components are outside the pressure vessel, they cannot be 

located in the bottom section of the pressure vessel. Instead, these components must be located in the bottom section of the viscometer.

Grace’s remaining arguments are unpersuasive. Grace 

argues that “top section” of the pressure vessel in limitation 4(a) means that “bottom section” in limitation 4(e) refers to the pressure vessel, and “top section” and “bottom 

section” in limitation 4(e) must both refer to the pressure 

vessel to facilitate communicating pressure between the 

two. Appellant’s Br. 58–59; Appellant’s Reply Br. 31. We 

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disagree. Limitation 4(e), consistent with our analysis 

above, can be understood as simply requiring that the enlarged chamber be positioned between the top section of the

pressure vessel and bottom section of the viscometer. 

Grace also argues that the district court’s interpretation of “means for driving” to include “magnetic coupling 

(magnet mount, gear box or motor, driving magnet, coupling magnet)” (1) excludes the patent’s preferred embodiments because certain components are outside of the 

pressure vessel and thus can cannot be located in the “bottom section,” Appellant’s Br. 63–65; (2) renders claim 14 

impossible by requiring the magnetic coupling to be inside 

the pressure vessel’s bottom section, Appellant’s Br. 65–66; 

and (3) requires the electric motor to be inside the pressurized bottom of the pressure vessel, even though a motor 

cannot work while submerged in drilling fluid, Appellant’s 

Br. 66–67. But for all of these arguments, Grace’s logic is 

circular. Each argument relies on Grace’s preferred interpretation that “bottom section” refers to the pressure vessel, not the viscometer. Under the correct interpretation 

that “bottom section” refers to the viscometer, the preferred 

embodiments are not excluded and there is no conflict with 

claim 14. 

Finally, Grace relies on claim 1 and a stipulation between the parties to argue that the ’877 patent uses the 

terms “lower section” and “bottom section” interchangeably 

to refer to the bottom section of the pressure vessel. Appellant’s Br. 60 (citing J.A. 1297). We disagree. The stipulation Grace cites only modifies claim 1, not claim 4, and only 

changes “bottom section” in claim 1 to “lower section” to 

address the lack of antecedent basis. Appellee’s Br. 50–51. 

Additionally, when Chandler argued at the Markman hearing that “lower section” in claim 1 refers to the pressurized 

device and “bottom section” in claim 4 refers to the viscometer, J.A. 1479–80 (75:8–76:10), Grace’s counsel asked the 

agreement to be withdrawn because Grace did not intend 

for the stipulation to be used against it in relation to 

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claim 4, J.A. 1489 (85:13–23). The stipulation thus does 

not make clear that the terms “lower section” and “bottom 

section” are used interchangeably in the ’877 patent, and 

we are not persuaded that the patentee intended the terms 

to be interchangeable.

For the foregoing reasons, we affirm the district court’s 

construction of “means for driving said rotor to rotate located in at least one bottom section.”

B. Grace’s Proposed Construction

We also reject Grace’s proposed alternate construction 

for the means for driving limitation. Grace’s proposed construction comprises two parts: (1) “means for driving” can 

be just the “magnet holder” alone because the magnet 

holder individually qualifies as a “means for driving,” Appellant’s Br. 67–68, Appellant’s Reply Br. 22–28; and 

(2) the “direct drive” alternative to magnetic coupling as 

the “means for driving” should be construed such that it 

“attaches in the bottom section to the rotor to rotate it,” 

rather than “at the bottom of the cell body,” Appellant’s Br. 

69. We disagree.

1. Magnet Holder 

Grace asserts that every structure involved in relaying 

power to the rotor individually qualifies as a separate

“means for driving.” See Appellant’s Reply Br. 26. But 

Grace misreads the specification. See, e.g., ’877 patent 

col. 5 ll. 42–47; see also id. at col. 8 ll. 24–30, col. 10 

ll. 36–42. The specification provides no details suggesting 

that the magnet holder, for example, could be solely responsible, without additional structure, for rotating the rotor. The other magnetic coupling components also are 

required to rotate the rotor.

Grace’s argument that its interpretation prevents excluding the preferred embodiments is, again, circular. The 

district court’s interpretation of “means for driving” only 

excludes the preferred embodiments if the claimed “bottom 

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section” refers to the pressure vessel, not the viscometer. 

But because we have determined that “bottom section” refers to the bottom section of the viscometer, the other components involved in the magnetic coupling “means for 

driving” may be located inside or outside the pressure vessel. See discussion supra Discussion § II.A. We thus disagree with Grace’s attempt to define the “means for driving” 

as any individual component that relays power to the rotor. 

2. Direct Drive

Grace argues that the district court erred in reading a 

limitation from the written description into the means for 

driving limitation by requiring the “direct drive” to be “at 

bottom of cell body.” Appellant’s Br. 69. Grace argues that 

means-plus-function claims must be limited to disclosed 

structures and equivalents, not locations of disclosed structures. Appellant’s Reply Br. 31–32. We disagree. 

The ’877 patent explains that magnetic coupling can be 

used to drive the rotor to rotate, or the rotor “could be 

driven to rotate with any means such as directly driven at 

the bottom of the cell body with dynamic seal, etc.” ’877 

patent col. 11 ll. 41–43 (emphasis added). The disclosed 

structure is, therefore, magnetic coupling or a direct drive 

at the bottom of the cell body, and known equivalents, consistent with the district court’s opinion. See Claim Construction Order, 2021 WL 2711987, at *7–8. We reject 

Grace’s attempt to disassociate the disclosed structure 

from the location of the disclosed structure. The specification indicates that the invention envisioned and claimed by 

the patentee was a direct drive attached to the bottom of 

the cell body. See, e.g., NOMOS Corp. v. BrainLAB USA, 

Inc., 357 F.3d 1364, 1367–68 (Fed. Cir. 2004) (affirming the 

district court’s construction of a “means for generating at 

least one ultrasound image” as requiring the ultrasound 

probe to be mounted to the treatment table by a fixation 

device). 

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CONCLUSION

We have considered Grace’s remaining arguments and 

do not find them persuasive. For the foregoing reasons, we 

vacate the district court’s determination that “enlarged 

chamber” is indefinite, vacate the district court’s invalidity 

determinations based thereon, and remand for further proceedings consistent with this opinion. We affirm the district court’s construction of “means for driving said rotor to 

rotate located in at least one bottom section” and the district court’s judgment based thereon. 

AFFIRMED-IN-PART, VACATED-IN-PART, AND 

REMANDED

COSTS

No costs.

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