Case: 19-1595    Document: 48     Page: 1   Filed: 04/10/2020




        NOTE: This disposition is nonprecedential.


   United States Court of Appeals
       for the Federal Circuit
                  ______________________

          REMBRANDT DIAGNOSTICS, LP,
               Plaintiff-Appellant

                             v.

   ALERE, INC., ALERE TOXICOLOGY SERVICES,
       INC., INNOVACON, INC., INSTANT
             TECHNOLOGIES, INC.,
            Defendants-Cross-Appellants
               ______________________

                   2019-1595, 2019-1648
                  ______________________

    Appeals from the United States District Court for the
 Southern District of California in No. 3:16-cv-00698-CAB-
 NLS, Judge Cathy Ann Bencivengo.
                  ______________________

                  Decided: April 10, 2020
                  ______________________

     JOSEPH F. JENNINGS, Knobbe, Martens, Olson & Bear,
 LLP, Irvine, CA, argued for plaintiff-appellant. Also rep-
 resented by JARED C. BUNKER; ASHLEY C. MORALES, San
 Diego, CA.

    JASON M. WILCOX, Kirkland & Ellis LLP, Washington,
 DC, argued for defendants-cross-appellants.      Also
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 2                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




 represented by HANNAH LAUREN BEDARD, JOHN C.
 O'QUINN; JAMES F. HURST, AMANDA J. HOLLIS, Chicago, IL.
                ______________________

     Before WALLACH, MAYER, and STOLL, Circuit Judges.
 STOLL, Circuit Judge.
     These appeals arise from an action for patent infringe-
 ment. Rembrandt Diagnostics, LP sued Alere, Inc., Alere
 Toxicology Services, Inc., Innovacon, Inc., and Instant
 Technologies, Inc. (collectively, “Alere”), alleging that
 Alere’s products infringe claims 3–6 and 10 of Rembrandt’s
 U.S. Patent No. 6,548,019, directed to devices for collecting
 and assaying biological fluid samples. Prior to trial, Rem-
 brandt stipulated to a judgment of noninfringement of
 claims 3–6 in light of the district court’s construction of a
 disputed claim limitation. During the trial, the district
 court construed another disputed claim limitation, and the
 jury rendered a verdict of noninfringement and no invalid-
 ity as to claim 10. Rembrandt now challenges the district
 court’s constructions of the two disputed claim limitations.
 Alere cross-appeals, requesting that this court order a new
 trial on validity of claim 10 if it remands for a new trial on
 infringement of that claim. Because we conclude that the
 intrinsic evidence supports Rembrandt’s proposed con-
 structions, we vacate the district court’s judgments and re-
 mand for further proceedings as to claims 3–6 and a new
 trial on both infringement and validity for claim 10.
                         BACKGROUND
                               I
     The ’019 patent “relates to immunoassay devices and
 methods for collection and assaying of biological fluids, par-
 ticularly urine.” ’019 patent col. 1 ll. 15–17; see also id.
 at Abstract. In particular, the patent discloses a “means
 for controlling assay sample fluid flow through an assay
 test strip,” wherein “fluid flow control is accomplished by
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                    3



 placing the assay test strip within a flow control channel in
 which the ambient pressure within the flow control chan-
 nel is maintained in substantial equilibrium with the am-
 bient pressure outside the flow control channel.”
 Id. at col. 1 ll. 40–47. “By avoiding the formation of a pres-
 sure gradient within the flow control channel,” the device
 of the ’019 patent minimizes “the risk of oversaturation of
 the test strip on introduction into an assay sample fluid.”
 Id. at col. 1 ll. 48–55.
     Figure 3 illustrates a front view of the preferred em-
 bodiment of the ’019 patent. Id. at col. 2 ll. 18–19.




 Id. Fig. 3. In this embodiment, the sample loading zone
 (30) of the assay test strip (22) partially extends beyond the
 opening of the flow control channel (34). The specification
 explains that “[a]ssay sample fluid control in this embodi-
 ment . . . is accomplished by disposing assay test strip 22
 within a flow control channel.” Id. at col. 5 ll. 57–59.
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 4                    REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




    Figure 4 illustrates a cross-section of the top portion of
 Figure 3. Id. at col. 2 ll. 20–21.




 Id. Fig. 4. The flow control channel “has five liquid imper-
 vious walls 35, 35A, 35B, 35C and backing 28, and one liq-
 uid pervious side consisting of an opening 36 through
 which sample loading zone 30 of assay test strip 22 pro-
 trudes.” Id. at col. 6 ll. 11–16; see also id. at col. 6 ll. 38–40
 (“Open end 36 has an opening 37 which is loosely fitted
 around test strip 22, whose sample loading zone 30 pro-
 trudes beyond opening 37.”).
      Figure 6 shows a “front view of an assay sample fluid
 collection device of the invention, into which is inserted the
 dipstick assay means of” Figures 3 and 4. Id. at col. 2
 ll. 24–27.




 Id. Fig. 6.
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                     5



     Claim 1, the only independent claim of the ’019 patent,
 recites the two disputed claim limitations:
     1. A device for collecting and assaying a sample of
     biological fluid, the device comprising:
     (a) a flow control channel defined by at least one
     liquid pervious side joined to liquid impervious
     sides, wherein the internal dimensions of the flow
     control channel are sufficient to permit placement
     therein of an assay test strip;
     (b) an assay test strip within the flow control chan-
     nel, wherein the assay test strip has a sample load-
     ing zone therein, and wherein further the assay test
     strip is disposed within the flow control channel so
     the sample fluid contacts the sample loading zone
     at a liquid pervious side of the flow control channel;
     and
     (c) a sample fluid container having a base, an open
     mouth, and walls connecting the base to the
     mouth;
     wherein the flow control channel is disposed inside
     the sample fluid container with the liquid pervious
     side oriented toward the base of the sample fluid
     container so that the assay sample fluid, when
     added to the container, is delivered to the sample
     loading zone of the assay test strip by entry
     through a liquid pervious side of the flow control
     channel without migration through an intermedi-
     ate structure, and wherein entry of fluid into the
     flow control channel creates an ambient pressure
     within the flow control channel equivalent to the
     ambient pressure outside of the flow control chan-
     nel, thereby eliminating a pressure gradient along
     which excess sample fluid could flow into the flow
     control channel.
 Id. at col. 8 l. 42–col. 9 l. 2 (emphases added).
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 6                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




     The claims at issue on appeal are dependent claims 3–
 6 and 10. Claim 10 requires that “all of the assay test
 strips” in the device “are disposed in a single flow control
 channel.” Id. at col. 10 ll. 5–6. None of the limitations of
 claims 3–6 or 10 is in dispute.
                               II
      Rembrandt accused four Alere urine test cup products
 of infringing claims 3–6 of the ’019 patent: the iCup DX Pro,
 AmediCheck, DrugSmart, and UScreen. 1 Rembrandt al-
 leged that these four products were copies of the preferred
 embodiment illustrated in Figures 3, 4, and 6 of the
 ’019 patent. Rembrandt also accused a fifth Alere urine
 test cup product—the iCup A.D.—of infringing claim 10.
 Rembrandt alleged that unlike the other four accused prod-
 ucts, the assay test strips of the iCup A.D. are disposed in
 a single flow control channel, as required by claim 10, and
 do not protrude from the end of the channel.
     As noted above, there are two claim limitations at issue
 on appeal: “the assay test strip is disposed within the flow
 control channel” in claim 1 and the claims that depend from
 claim 1 (the “disposed within” limitation); and “entry of
 fluid into the flow control channel creates an ambient pres-
 sure within the flow control channel equivalent to the am-
 bient pressure outside of the flow control channel” in



     1    In a parallel inter parties review proceeding, Rem-
 brandt disclaimed claims 1, 9, and 11–15 of the ’019 patent,
 leaving only claims 2–5 in dispute. Because the Board did
 not institute review of all claims and grounds in the IPR
 petition, this court vacated the Board’s patentability deter-
 minations as to claims 2–5, and remanded for the Board to
 review all claims and grounds included in the petition pur-
 suant to SAS Institute, Inc. v. Iancu, 138 S. Ct. 1348 (2018).
 Alere, Inc. v. Rembrandt Diagnostics, LP, 791 F. App’x 173,
 178 (Fed. Cir. 2019).
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                    7



 claim 1 and the claims that depend from claim 1 (the
 “equivalent to” limitation).
     Prior to trial, the district court construed the “disposed
 within” limitation to require that “the assay test strip is
 disposed entirely within the flow control channel.” Rem-
 brandt Diagnostics, L.P. v. Innovacon, Inc., No. 16–698,
 2017 WL 6059129, at *4 (S.D. Cal. Dec. 7, 2017) (Claim
 Construction Op.) (emphasis added). Rembrandt had pro-
 posed that the limitation should be “accorded its plain and
 ordinary meaning” and that, to the extent the court con-
 strued the limitation, it should mean “the assay test strip
 is placed or arranged within the flow control channel.”
 J.A. 2932. The district court rejected this proposed con-
 struction, which would allow the assay test strip to “pro-
 trude at the pervious end such that the sample loading
 zone of the strip extends beyond the channel in the manner
 described in the specification and depicted in Figure 3.”
 Claim Construction Op., 2017 WL 6059129, at *3 (citations
 omitted). While acknowledging that a “claim interpreta-
 tion that excludes a preferred embodiment from the scope
 of the claim is rarely, if ever, correct,” the district court
 nonetheless determined that the “unambiguous” claim lan-
 guage and the prosecution history “result[ed] in the exclu-
 sion of a preferred embodiment that teaches the loading
 zone can protrude from the channel.” Id. at *4 (citations
 omitted).
      Following the district court’s construction of the “dis-
 posed within” limitation, Rembrandt stipulated to the dis-
 trict court’s entry of judgment that none of accused
 products iCup DX Pro, AmediCheck, DrugSmart, or
 UScreen infringed claims 3–6 of the ’019 patent “because
 the test strips in such products are not ‘disposed entirely
 within the flow control channel.’” Pretrial Order at 3, Rem-
 brandt Diagnostics, LP v. Alere, Inc., No. 16–698 (S.D. Cal.
 Nov. 19, 2018), ECF No. 312.
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 8                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




      The case then proceeded to a jury trial solely concern-
 ing the validity of claim 10 and the iCup A.D. product’s al-
 leged infringement thereof. During the trial, the district
 court construed the “equivalent to” limitation in claim 1 to
 mean “equal to.” J.A. 10941 at 434:12–17. The district
 court rejected Rembrandt’s proposed construction of the
 disputed limitation to mean “in equilibrium with.” The dis-
 trict court thereafter instructed the jury that “equivalent
 to” was defined as “equal to.” The jury found that the iCup
 A.D. product did not infringe claim 10, and that claim 10
 was not invalid for anticipation or obviousness.
    Rembrandt and Alere appeal. We have jurisdiction
 pursuant to 28 U.S.C. § 1295(a)(1).
                         DISCUSSION
     We start by addressing Rembrandt’s challenge to the
 district court’s constructions of the two disputed claim lim-
 itations: the “disposed within” limitation and the “equiva-
 lent to” limitation. We then turn to Alere’s cross-appeal, in
 which it contends that if this court remands for a new trial
 on infringement for claim 10, it should order a new trial on
 validity as well.
                               I
      Claim construction based on the intrinsic evidence is a
 question of law that this court reviews de novo. Trustees of
 Columbia Univ. v. Symantec Corp., 811 F.3d 1359, 1362
 (Fed. Cir. 2016). “The construction of claim terms based on
 the claim language, the specification, and the prosecution
 history are legal determinations.” Id. The two claim con-
 struction disputes in this case present close questions.
 Based on our review of the claim language, specification,
 and prosecution history, however, we conclude that the dis-
 trict court erred in construing the disputed claim limita-
 tions.
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                     9



                               A
      We consider first Rembrandt’s challenge to the district
 court’s construction of “disposed within.” At the outset, we
 recognize that the language of claim 1 is ambiguous. The
 parties’ arguments focus on two specific phrases in claim 1.
 First, the device of claim 1 comprises an “assay test strip”
 that is “disposed within the flow control channel so the
 sample fluid contacts the sample loading zone at a liquid
 pervious side of the flow control channel.” ’019 patent col. 8
 ll. 42–54 (emphases added). Second, the device is arranged
 in such a way that the “assay sample fluid, when added to
 the container, is delivered to the sample loading zone of the
 assay test strip by entry through a liquid pervious side of
 the flow control channel without migration through an in-
 termediate structure.” Id. at col. 8 ll. 57–64 (emphasis
 added).
     Both parties present reasonable arguments about how
 the disputed limitation should be understood based on this
 claim language. Alere contends that the district court’s
 construction is correct because if the test strip were to “pro-
 trude” from the flow control channel, the sample fluid
 would contact the strip before the fluid reaches the chan-
 nel. Thus, according to Alere, the fluid would not “contact”
 the test strip’s loading zone “at” the liquid pervious side of
 the channel, as required by claim 1; instead, the contact
 would happen on the protruding portion of the strip outside
 of the channel. In addition, the fluid would not be “deliv-
 ered” to the test strip’s loading zone “by entry through” the
 liquid pervious side of the channel, as also required by
 claim 1.
     Rembrandt’s broader construction—which encom-
 passes devices with protruding test strips—also finds sup-
 port in the claim language. Rembrandt contends that
 claim 1 does not require that the sample fluid contact the
 test strip’s loading zone “first and only precisely at the
 opening of the flow control channel and nowhere else.”
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 10                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




 Appellant’s Resp. Br. 5 (emphasis in original). In Rem-
 brandt’s view, “at” is not limited to “the singular spot of
 entry to the flow control channel” and, in fact, such a con-
 struction “would exclude a device in which the test strip is
 entirely within the flow control channel but does not extend
 to being flush with it.” Id. Rembrandt also contends that
 claim 1 does not require that the “fluid be delivered to the
 test strip ‘only’ by entry through the channel opening and
 nowhere else.” Id. In sum, the claim language does not
 definitively support one construction over the other.
       We turn next to the specification, which “is the single
 best guide to the meaning of a disputed term.” Phillips
 v. AWH Corp., 415 F.3d 1303, 1315 (Fed. Cir. 2005) (quot-
 ing Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576,
 1582 (Fed. Cir. 1996)). There is no dispute that the district
 court’s construction excludes the preferred embodiment of
 the ’019 patent, as depicted in Figures 3 and 4. Claim Con-
 struction Op., 2017 WL 6059129, at *4. By contrast, Rem-
 brandt’s proposed construction encompasses the preferred
 embodiment. There is also no dispute that, in describing
 the preferred embodiment, the specification uses nearly
 identical language as the disputed claim language. Com-
 pare ’019 patent col. 8 ll. 51–52 (“the assay test strip is dis-
 posed within the flow control channel” (emphasis added)),
 with id. at col. 5 ll. 57–59 (“Assay sample fluid control in
 this embodiment of the invention is accomplished by dis-
 posing assay test strip 22 within a flow control channel
 . . . .” (emphases added)).
     Turning next to the prosecution history, we are not per-
 suaded that the prosecution history includes a clear and
 unmistakable surrender of claims directed to a preferred
 embodiment in which test strips protrude. Nor are we per-
 suaded that any of the inventors’ statements otherwise re-
 quire a claim construction that would omit a preferred
 embodiment.
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                     11



     Claim 1 was initially drafted to recite a method com-
 prising the step of “disposing an assay test strip within the
 flow control channel,” wherein the “assay test strip is dis-
 posed within the flow control channel so the sample loading
 zone is flush with, or protrudes from, a liquid pervious side
 of the flow control channel.” J.A. 11517 (emphasis added).
 The Patent Office rejected claim 1 as anticipated by, and
 for obviousness-type double patenting over, related
 U.S. Patent Application No. 09/192,969. The ’969 applica-
 tion issued as U.S. Patent No. 6,379,620 (Tydings).
     Tydings shares an inventor with the ’019 patent and
 discloses and claims a device that Rembrandt refers to as
 the inventors’ “first generation drug test cup design.” Ap-
 pellant’s Br. 8. Like the device recited in claim 1 of the
 ’019 patent, Tydings discloses a device that uses assay test
 strips, as illustrated in Figure 3 of Tydings:




 Tydings Fig. 3. The prior art Tydings device is also de-
 picted in Figures 1 and 2 of the ’019 patent.
      The Tydings device uses a wicking material, such as
 filter paper or fiber glass, which “extends substantially the
 full length of the backing” of the cup. Id. at col. 2 ll. 40–45.
 As shown in Figure 3, the “top portion of the reagent strip
 12 is bent over the top edge 15 of the backing 8 and over-
 lapped onto the wicking paper 10.” Id. at col. 2 ll. 65–67.
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 12                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




 Urine “wicks up the wicking material 10 until it reaches
 the overlapped portions of the assay strips 12,” and then
 “wicks over the top edge of the backing 8 and down the as-
 say strips 12.” Id. at col. 3 ll. 25–28. “The urine wicking
 down the assay strips 12 will react with the chemical
 agents” on the strip and “will give positive, negative or in-
 conclusive test results.” Id. at col. 3 ll. 28–31.
     In its response to the examiner’s office action, the ap-
 plicants distinguished Tydings on the ground that the
 claimed invention:
      provides a flow control channel whereby the sam-
      ple is delivered directly to the sample loading
      zone 30 of assay strip 22 through a liquid pervious
      side 36 (as opposed to having the fluid migrate
      through an intermediate structure, such as wick-
      ing material 10 of FIGS. 1 and 2 [the ’969 device]
      . . . ).
 J.A. 11613 (underlining omitted). In addition, the appli-
 cants amended claim 1 to recite a device and added the re-
 quirement that “the assay sample fluid, when added to the
 container, is delivered directly to the sample loading zone
 through a liquid pervious side of the flow control channel.”
 J.A. 11601 (emphasis added).
     The patent examiner was not convinced and main-
 tained the rejections based on Tydings. The applicants
 thereafter amended claim 1 to recite, in relevant part, that
 “the assay test strip is disposed within the flow control
 channel so the sample fluid contacts the sample loading
 zone at a liquid pervious side of the flow control channel.”
 J.A. 11674 (emphases added). At the same time, the appli-
 cants removed the requirement that the test strip’s sample
 loading zone “is flush with, or protrudes from,” a liquid per-
 vious side of the channel. Id. The applicants further
 amended the claim to recite that fluid is “delivered directly
 to the sample loading zone of the assay test strip through
 a liquid pervious side of the flow control channel without
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                  13



 migration through an intermediate structure.” Id. (empha-
 sis added). The applicants reiterated to the examiner that,
 in contrast to the Tydings device, the claimed invention did
 not use an intermediate structure.
     Shortly thereafter, the applicants further amended
 claim 1 to recite that “the assay sample fluid, when added
 to the container, is delivered to the sample loading zone of
 the assay test strip by entry through a liquid pervious side
 of the flow control channel without migration through an
 intermediate structure,” and removed the requirement
 that the fluid is delivered “directly” to the loading zone.
 J.A. 11688 (emphasis added). The applicants explained
 that their invention “improves upon previous devices by
 preventing the flooding of test strips by constructing a flow
 channel around the strips,” and that the liquid pervious
 side of the channel “limit[s] the rate at which sample will
 flow into the channel to contact the sample loading zone on
 the assay strips.” J.A. 11686 (emphases added).
     Alere’s argument that the applicants’ amendments
 during prosecution support a narrower construction has
 some merit. Ultimately, however, we disagree with Alere
 and the district court that the applicants narrowed the
 scope of claim 1 during prosecution to cover only devices
 with test strips that are disposed “entirely” within the flow
 control channel. In particular, the applicants did not
 merely remove “protrudes from” in claim 1; rather, they re-
 moved “is flush with, or protrudes from.” J.A. 11674. In
 addition, the applicants never distinguished the Tydings
 device (or any other prior art device) on the ground that the
 claimed test strips cannot protrude beyond the channel.
 Instead, the applicants expressly distinguished the
 Tydings device on the basis that Tydings used an interme-
 diate structure, and amended the claims to exclude the use
 of such intermediate structure. And although the addi-
 tions of the “by entry” and “contact . . . at” language in
 claim 1 were made in conjunction with, or shortly after, re-
 moval of the “flush with, or protrudes from” language,
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 14                 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




 these additions were also made when the applicants
 amended claim 1 to exclude the use of an intermediate
 structure. Alere emphasizes that claim 1 was amended to
 exclude the protruding strips embodiment while still cov-
 ering the flush strips embodiment based on the added lan-
 guage that “the sample fluid contacts the sample loading
 zone at a liquid pervious side of the flow control chan-
 nel.” But, as we have already discussed, this language is
 at best ambiguous and does not require a construction that
 the strips must be contacted only at a particular location.
      Contrary to the district court’s suggestion, Elekta In-
 strument S.A. v. O.U.R. Scientific International, Inc.,
 214 F.3d 1302 (Fed. Cir. 2000), does not “compel[] adopting
 [a] construction excluding [the preferred] embodiment” of
 protruding strips based on the applicants’ amendments in
 this case. Claim Construction Op., 2017 WL 6059129, at *4
 (citing Elekta, 214 F.3d at 1308). In Elekta, the claim at
 issue expressly required gamma units with radiation
 sources “only within a zone extending between latitudes
 30°–45°.” 214 F.3d at 1306. The preferred embodiment
 disclosed sources between 0°–45°, and the district court
 construed the claim to cover sources beginning at 0° and
 extending to a point between 30°–45°. Id. at 1306–07. We
 held that the district court’s construction was inconsistent
 with the “unambiguous” claim language, which “controls
 over any contradictory language in the written descrip-
 tion.” Id. at 1308. In light of the unambiguous claim lan-
 guage and the prosecution history—in which the
 applicants expressly limited their invention to sources lo-
 cated exclusively between 30° and 45°—this court held that
 this was the “rare case” in which the construction must ex-
 clude the preferred embodiment. Id. Here, in contrast, nei-
 ther the claim language nor the prosecution history
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                  15



 demonstrates that claim 1 is “susceptible of only one rea-
 sonable construction.” 2 Id.
      We have considered Alere’s other arguments, but we do
 not find them persuasive. Although Rembrandt’s chal-
 lenge presents a close issue, we conclude that the claim lan-
 guage, specification, and prosecution history are more
 aligned with a broader construction that would not exclude
 the preferred embodiment. Accordingly, we construe the
 “disposed within” limitation to mean “the assay test strip
 is placed or arranged within the flow control channel.”
                              B
     We next consider Rembrandt’s challenge to the district
 court’s construction of the “equivalent to” limitation, along
 with the district court’s jury instruction based thereon.
 “An erroneous instruction regarding claim interpretation
 that affects the jury’s decision on infringement is grounds
 for a new trial.” Ecolab, Inc. v. Paraclipse, Inc., 285 F.3d
 1362, 1373 (Fed. Cir. 2002). “A party seeking to alter a
 judgment based on erroneous jury instructions must estab-
 lish that ‘those instructions were legally erroneous,’ and
 that ‘the errors had prejudicial effect.’” Id. (quoting Ad-
 vanced Display Sys., Inc. v. Kent State Univ., 212 F.3d
 1272, 1281 (Fed. Cir. 2000)). Whether a jury instruction is
 legally erroneous is a question of law. Id. (citing Brooktree




     2   Alere cites North American Container, Inc.
 v. Plastipak Packaging, Inc., 415 F.3d 1335 (Fed. Cir. 2005)
 and Uship Intellectual Properties, LLC v. United States,
 714 F.3d 1311 (Fed. Cir. 2013), for the proposition that
 claim limitations may be construed to exclude a preferred
 embodiment if the prosecution history compels that result.
 Unlike this case, each of those cases involved narrowing
 amendments or remarks that clearly removed the pre-
 ferred embodiments from the claim scope.
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 16                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




 Corp. v. Advanced Micro Devices, Inc., 977 F.2d 1555, 1570
 (Fed. Cir. 1992)).
      This claim construction issue also presents a close
 question. Based on our review of the claim language, spec-
 ification, and prosecution history, however, we conclude
 that Rembrandt’s proposed construction of the “equivalent
 to” limitation to mean “in equilibrium with” is more con-
 sistent with the intrinsic record than the construction
 adopted by the district court. We also conclude that Rem-
 brandt has demonstrated that the jury instruction was er-
 roneous and prejudicial.
      The plain claim language suggests a broader meaning
 of “equivalent to” than “equal to.” Claim 1 recites, in rele-
 vant part, that the “entry of fluid into the flow control chan-
 nel creates an ambient pressure within the flow control
 channel equivalent to the ambient pressure outside of the
 flow control channel, thereby eliminating a pressure gradi-
 ent along which excess sample fluid could flow into the flow
 control channel.” ’019 patent col. 8 l. 64–col. 9 l. 2 (empha-
 sis added). Similar to the oft-used claim term “substan-
 tially,” we consider “equivalent,” as used in claim 1, to be a
 term of degree that does not require mathematical preci-
 sion. See Ecolab, Inc. v. Envirochem, Inc., 264 F.3d 1358,
 1367 (Fed. Cir. 2001) (“[T]he term ‘substantially’ is a de-
 scriptive term commonly used in patent claims to ‘avoid a
 strict numerical boundary to the specified parame-
 ter.’” (quoting Pall Corp. v. Micron Seps., 66 F.3d 1211,
 1217 (Fed. Cir. 1995))). Indeed, as Rembrandt correctly ob-
 serves, the patent law doctrine of equivalents refers to the
 legal comparison of two elements that are, in fact, different,
 which supports that “equivalent” is not limited to “equal.”
 If the applicants meant “equal,” they would have used the
 word “equal” rather than the broader word “equiva-
 lent.” Claim 1 neither uses the term “equal” nor refers to a
 numerical measurement, numerical comparison between
 pressures, or even the pressure unit of measurement—pas-
 cals.
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                          17



     The specification also supports a broader interpreta-
 tion of the claim language. The specification repeatedly
 uses terms other than “equal” to describe achieving the
 claimed result of “eliminating a pressure gradient along
 which excess sample fluid could flow into the flow control
 channel.” For example, the specification teaches:
     By maintaining substantial ambient pressure equi-
     librium about the flow control channel, no pressure
     gradient is allowed to form along which fluid out-
     side the flow control channel will flow into the flow
     control channel.
 Id. at col. 6 ll. 28–31 (emphasis added); see also id. at Ab-
 stract, col. 1 ll. 42–47, col. 5 ll. 57–64, col. 5 l. 64–col. 6 l. 2,
 col. 6 ll. 23–31, 47–51 (referring to “equilibrium” or “sub-
 stantial equilibrium”). Like claim 1, the specification never
 uses the term “equal” when discussing air pressure, nor
 does it mention pascals, pressure tests, or numerical meas-
 urements. Thus, the specification further supports Rem-
 brandt’s construction, which “captures immaterial and
 insubstantial differences in the two pressures,” Appellant’s
 Br. 56, over a construction that requires mathematical
 equality.
     We understand the district court’s view that “equiva-
 lent” could mean “equal” given the applicants’ statements
 during prosecution about the pressures inside and outside
 the channel being “equalized.” Specifically, the applicants
 argued that “the liquid pervious side of the channel serves
 as a pressure equalizer,” J.A. 11611 (emphasis added), and
 that the “present invention utilizes equalized pressure,”
 J.A. 11650 (emphasis added). But even “equalized pres-
 sure” does not mean the pressures are mathematically,
 precisely equal. For instance, when explaining the “ambi-
 ent pressure” limitation and distinguishing the Tydings de-
 vice, the applicants described their invention as using a
 flow control channel to create a “pressure equilibrium.”
 J.A. 11672; see also J.A. 11611 (“The present invention
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 18                  REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




 improves upon previous devices by preventing the flooding
 of test strips by constructing a flow channel so the air pres-
 sure within it stays in substantial equilibrium with the air
 pressure outside of it.” (emphasis added)).
     We have considered Alere’s other arguments, but we do
 not find them persuasive. We conclude that the district
 court’s construction imposes a mathematical or numerical
 rigor of exactness that is not supported by the intrinsic ev-
 idence. Accordingly, we construe the “equivalent to” limi-
 tation to mean “in equilibrium with.” We also hold that the
 jury instruction that included the district court’s construc-
 tion was prejudicial and requires the verdict of nonin-
 fringement of claim 10 to be set aside.
                               II
     We next turn to the issue raised in Alere’s cross-appeal.
 Because we have determined that the district court’s con-
 struction of the “equivalent to” limitation was erroneous,
 we conclude that a new trial will be necessary to determine
 whether the asserted prior art anticipates or renders obvi-
 ous claim 10 under the correct construction of the “equiva-
 lent to” limitation.
      “The Federal Rules of Civil Procedure allow the courts
 to grant partial new trials so long as the issues are ‘distinct
 and separable.’” Commil USA, LLC v. Cisco Sys., Inc.,
 720 F.3d 1361, 1371 (Fed. Cir. 2013) (citing Fed. R. Civ.
 P. 59), vacated in part, 575 U.S. 632 (2015). “A court’s au-
 thority to grant a partial new trial is likewise constrained
 by the Seventh Amendment.” Id. (citing Gasoline Prod. Co.
 v. Champlin Refining Co., 283 U.S. 494, 500 (1931)).
 “Where the practice permits a partial new trial, it may not
 properly be resorted to unless it clearly appears that the
 issue to be retried is so distinct and separable from the oth-
 ers that a trial of it alone may be had without injus-
 tice.” Id. (quoting Gasoline Prod., 283 U.S. at 500).
 “A partial new trial should not be granted where the issues
 to be retried are ‘so interwoven’ with other issues in the
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 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.                 19



 case ‘that the former cannot be submitted to the jury inde-
 pendently of the latter without confusion and uncer-
 tainty.’” Id. (quoting Gasoline Prod., 283 U.S. at 500).
      It is true, as Rembrandt asserts, that infringement and
 validity are distinct issues and that this court previously
 stated that it “routinely orders a partial new trial on in-
 fringement, while upholding an earlier verdict on valid-
 ity.” Commil, 720 F.3d at 1371 (first citing Cardiac
 Pacemakers, Inc. v. St. Jude Med., Inc., 381 F.3d 1371,
 1374 (Fed. Cir. 2004); then citing Comaper Corp. v. Antec,
 Inc., 596 F.3d 1343, 1354–55 (Fed. Cir. 2010)). Rembrandt
 contends that the correct construction of “equivalent to”
 was “not material to the jury’s rejecting Alere’s challenge
 to the validity of claim 10” because the evidence showed
 that the asserted prior art reference “failed to meet the
 ‘equivalent to’ limitation even under the correct construc-
 tion.” Appellant’s Resp. Br. 33.
      The testimony of Alere’s expert, however, demon-
 strates that the infringement and validity issues are inter-
 twined. See, e.g., J.A. 11077–78 at 570:5–571:9; J.A. 11117
 at 610:18–20. Alere would suffer an injustice if it were not
 permitted to challenge the validity of claim 10 under Rem-
 brandt’s proposed construction in a new trial if Rembrandt
 has another opportunity to prove infringement. See Com-
 mil, 720 F.3d at 1371. Although Rembrandt cites testi-
 mony by its expert that the asserted prior art reference
 does not disclose “a flow control channel and flow control
 capability as required by claim 10” to show that a new trial
 on invalidity is unnecessary, Appellant’s Resp. Br. 36 (cit-
 ing J.A. 11130–32 at 623:25–625:9), Alere identifies con-
 trary testimony of both parties’ experts that the reference
 does, in fact, disclose all the elements of claim 10, Cross-
 Appellant’s Resp. Br. 4–6 (citing J.A. 11068 at 561:4–21;
 J.A. 11078–81 at 571:10–574:4; J.A. 11138–41 at 631:13–
 634:15). Thus, a reasonable jury could find based on the
 evidence that the asserted prior art teaches the “equivalent
 to” limitation under the correct construction.
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 20                 REMBRANDT DIAGNOSTICS, LP v. ALERE, INC.




     Accordingly, we remand for a new trial on both in-
 fringement and validity of claim 10 under the correct con-
 struction of the “equivalent to” limitation.
                         CONCLUSION
      For the foregoing reasons, we vacate the district court’s
 judgment of noninfringement as to claims 3–6 and remand
 for further proceedings under the proper construction of
 the “disposed within” limitation. We also vacate the dis-
 trict court’s judgment of noninfringement and validity as
 to claim 10 and remand for a new trial on the issues of in-
 fringement and validity of that claim under the proper con-
 struction of the “equivalent to” limitation.
                VACATED AND REMANDED
                            COSTS
      Costs to Appellant.
