## United States Court of Appeals for the Federal Circuit

04-1414

BIAGRO WESTERN SALES, INC. and THE REGENTS OF THE UNIVERSITY OF CALIFORNIA, Plaintiffs-Appellants,

v.
GROW MORE, INC., Defendant-Appellee.

Mark D. Miller , Kimble, MacMichael & Upton, of Fresno, California, argued for plaintiffs-appellants. Wi th him on the brief were Robert W. Branch and Mary Ann Bluhm

. Alan L. Unikel , Seyfarth Shaw LLP, of Chicago, Illinois, argued for defendantappellee. With him on the brief was Joseph R. Lanser

. Appealed from: United States District Court for the Eastern Dis trict of California Senior Judge Robert E. Coyle

## United States Court of Appeals for the Federal Circuit

04-1414 BIAGRO WESTERN SALES, INC. and THE REGENTS OF THE UNIVERSITY OF CALIFORNIA, Plaintiffs-Appellants,

v. GROW MORE, INC., Defendant-Appellee.

__________________________ DECIDED: September 13, 2005

__________________________ Before GAJARSA, Circuit Judge , PLAGER, Senior Circuit Judge , and DYK, Circuit Judge

. PLAGER, Senior Circuit Judge

. In this patent infringement case, Biagro Western Sales, Inc. (“Biagro”) and The Regents of the University of California (“The Regents”) sued Grow More, Inc. (“Grow More”) in the United States District Court for t he Eastern District of Ca lifornia. At issue is U.S. Patent No. 5,830, 255 (“the ’255 patent”), which is entitled “Formulation of Phosphorus Fertilizer for Plants.” The Regents are the assi gnee and Biagro is the exclusive licensee of the ’255 patent. On cross-motions for summaryjudgment, the trial court held that Grow More did not literally infringe the claims of the patent. The trial cour t further held that there was no infringement under the doctrine of equival ents. Judgment was awarded to Grow More. We affirm the judgment of the trial court.BACKGROUND The United States Patent and Trademar k Office (“PTO”) issued the ’255 patent on November 3, 1998. At t he request of The Regents, to whom the patent had been assigned, the PTO undertook a reexamination and issued a reexamination certificate on July 11, 2000. As a result of the reexamination, all of the independent claims were amended by adding a limitat ion, originally in several dependent claims, relating to the amount of phosphorous-containing acid or salt thereof in the fertilizer formulation. After reexamination, claim 1, represent ative of the independent claims of the ’255 patent, read: A concentrated phosphorus fertilizer comprising a buffered composition comprising at least one phosphorous-contai ning acid or salt thereof such that when said composition is dilut ed with water having a pH of about 6.5 at a ratio of about 1 part fertilizer to about 40 parts water, there is formed a substantially fully solubilized use- dilution fertilizer having a foliageacceptable pH for phosphorus uptake and wherein said phosphorouscontaining acid or salt thereof is present in an am ount of about 30 to about 40 weight percent

. The emphasized language was added dur ing reexamination to distinguish the claimed invention over prior art. That added limitation is the focus of the dispute in this case. The term “phosphorous” is an adjectival m odifier describing certain compounds containing the element phos phorus (P). In the patent, the term “phosphorouscontaining acid” is used to refer to a gr oup of acids that includes phosphorous acid (H 3 PO 3 ), among other acids. ’255 patent, col. 3, ll. 56-60. The patent also states that the formulations in the patent are expressed in terms of weight-to-volume, instead of weight-to-weight, and therefore the term “weight percent” as us ed in the claims refers to a weight-to-volume percentage. Id. at col. 6, l. 67.

04-1414 2Grow More’s accused product is a phosphor us fertilizer named Phos-Pro. PhosPro is made by mixing phosphorous acid (H 3 PO 3 ) with potassium hydroxide (KOH) and water. The reaction results in a solu tion containing two phosphorous acid salts— dipotassium monohydrogen phosphite (K 2 HPO 3 ) and potassium dihydrogen phosphite (KH 2 PO 3 ), referred to in abbreviated form as dipotassium phosphite and potassium phosphite. A third phosphite, tripotassium phosphite (K 3 PO 3 ), is present in trace amounts. However, and import antly, the final Phos-Pro pr oduct does not contain any phosphorous acid as such. Biagro, as the exclusive lic ensee of the ’255 patent, fil ed this patent infringement suit against Grow More in July 2000, shortl y after the PTO completed reexamination of the patent. Grow More f iled counterclaims for decl aratory judgments of noninfringement and invalidity and for unfair com petition under Californi a state law. The Regents were eventually joined as a plaintiff. 1 The parties filed cross-motions for summary judgment on the question of infringement. At issue was the meaning of the added limitation spec ifying that in the claimed fertilizer composit ion there was a “phosphorous-c ontaining acid or salt thereof

. . . present in an amount of about 30 to about 40 weight percent.” Biagro argued that the limitation can be met in an accused product by calculating a ‘chemical equivalent’ amount of phosphorous -containing acid, based on the chemical composition of the fertilizer. In the case of the accused Grow More fertilizer, that would be the same as the amount of phosphorous-containing acid used in the initial manufacture of the product. Grow More argued to the contrary that the limitation referre d to the amount of

1 Plaintiffs Biagro and The Regents will be referred to collectively as “Biagro” throughout the remainder of this opinion.

04-1414 3phosphorous-containing acid or salt actually present in the final fertilizer product. The trial court construed the limit ation as Grow More proposed and, since the Grow More final product contained no phosphorous-containing acid, held for Grow More on that issue. The trial court concluded further that, with regard to the content of acid salts in the fertilizer, a fertilizer containing two or more phosphorous-containing salts comes within the literal scope of the claim only if the aggregate amount of such salts is between about 30 and about 40 weight percent. Based on tests and calculations made by Biagro’s expert, the concent ration of potassium phosphite in Phos-Pro is 40.3%, and the concentration of dipotassium phosphite is 19.0%. Grow More’s calculations indicated the phosphite content to be slightly higher based on a differ ent specific gravity used to convert weight-to-weight percent ages to weight-to-volume percentages. According to Grow More’s calculations, the weight-to-volume perc entages are 42.2% for potassium phosphite and 19.9% for dipotassium phosphite. Thus the total phosphite concentration in the accused product is between 59.3% and 62.1%, depending on which party’s calculations are used. Since the aggregate concentration of the tw o phosphites in the accused product is at least 59.3% weight percent, well out side the claimed range and thus not literally infringing, the question was whether the amount of salts could be considered infringing under the doctrine of equivalent s, that is, whether 60(+/-)% could be considered the equivalent of about 30 to about 40%. The trial court chose not to address that question, but instead held for Grow More on the gr ound that, in light of the amended claims, prosecution history estoppel ac ted as a complete bar to a claim of infringement under

04-1414 4the doctrine of equivalents according to this court’s en banc decision in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. , 234 F.3d 558 (Fed. Cir . 2000) (en banc) (“ Festo I ”), the law in effect at the time. The trial court granted judgm ent for Grow More. Biagro W. Sales, Inc. v. Grow More, Inc. , No. CV-F-00-6105 (E.D. Cal. Oct. 18, 2001). Biagro filed two motions for reconsiderat ion directed to the issue of whether a proper claim construction should permit use of the chemical equivalent analysis. The trial court denied both of these mo tions for reconsideration. Biagro W. Sales, Inc. v. Grow More, Inc. , No. CV-F-00-6105 (E.D. Cal. Aug. 15, 2002); Biagro W. Sales, Inc. v. Grow More, Inc. , No. CV-F-00-6105 (E.D. Cal. Apr. 9, 2003). Meanwhile, the Supreme Court vaca ted and remanded our decision in Festo I

. Festo Corp. v. Shoketsu Ki nzoku Kogyo Kabushiki Co. , 535 U.S. 722 (2002) (“ Festo II ”). Since final judgment had not ye t been entered, the trial judge a llowed the parties to file briefs addressing whether Bi agro could rebut the new ‘ Festo presumption’ that the patentee had surrendered all subject matter betw een the original claim limitation and the amended claim limitati on. While the trial court was considering the matter, we rendered our second en banc decision in the Festo case, this time on remand from the Supreme Court. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. , 344 F.3d 1359 (Fed. Cir. 2003) (en banc) (“ Festo III ”). Biagro argued before the tr ial court that it could overcome the Festo presumption in two of the ways set forth by the Supreme Court in Festo II and further explained in Festo III . The trial court rejected both arguments. Biagro W. Sales, Inc. v. Grow More, Inc. , No. CV-F-00-6105 (E.D. Cal. Mar. 30, 2004). The trial court therefore denied Biagro’s motion for reconsideration based on rebuttal of the Festo presumption.

04-1414 5The parties stipulated to di smissal without prejudice of Grow More’s counterclaim for unfair competition. The trial court had previously deemed Grow More’s counterclaim for invalidity withdrawn without prejudice. Thus there were no pending, unresolved claims, and the trial court entered final judgment for Grow More. Biagro filed a timely appeal. We have jurisdiction pursuant to 28 U.S.C. § 1295(a)(1). DISCUSSION A. Standard of Review We review a grant of summary judgment without deference to the trial court. Conroy v. Reebok Int’l, Ltd. , 14 F.3d 1570, 1575 (Fed. Cir. 1994). Summary judgment is appropriate if there is no genuine issue as to any material fact and the moving party is entitled to judgment as a matter of law. Fed. R. Civ. P. 56(c). An infringement analysis proceeds first to claim construction to determine the scope and meaning of the asserted claims, and second to a comparis on of the properly construed claims with the allegedly infringi ng product to determine whether the product embodies every limitation of the claims. Cybor Corp. v. FAS Techs., Inc. , 138 F.3d 1448, 1454 (Fed. Cir. 1998) (en banc). Claim construction is a matter of law over which we exercise independent review. Id. at 1456. Whether an accused device or method infringes a claim, either liter ally or under the doctrine of equi valents, is a question of fact. Bai v. L & L Wings, Inc. , 160 F.3d 1350, 1353 (Fed. Cir. 1998). Prosecution history estoppel is a legal limitation on t he doctrine of equivalents. Festo III , 344 F.3d at 1368. Issues relating to the application and scope of prosecution history estoppel, including whether the presum ption of surrender of subject matter has

04-1414 6arisen and whether it has been rebutted, are questions of law to be decided by the
court. Id. Rebuttal of the presumption may be subject to underlying factual issues, which may properly be decided by the court. Id. at 1368 n.3. B. Claim Construction On appeal, Biagro challenges the trial court’ s construction of the claim limitation “wherein said phosphorous-containing acid or sa lt thereof is pres ent in an amount of about 30 to about 40 weight percen t.” As it did before the trial court, Biagro makes two separate arguments, each one corresponding to a different theory. We address each theory in turn, and we affirm the trial court’s claim construction under both.
1. Biagro first argues that the amount of phosphorous-containing acid in the claim limitation refers to a chemical equivalent amount rather than, as the trial court held, the amount of phosphorous-containing ac id actually present in the final fertilizer product. According to Biagro, the ‘chemical equiva lent’ is a calculated amount of phosphorouscontaining acid regardless of whether phosphorous-containing acid is actually present in the fertilizer, that is, the amount of phosphorous-containing ac id that would react to make the final fertilizer. If the amount of phosphorous-containi ng acid that was used to create the product is unknown, the chemic al equivalent amount can be derived by testing the final product and performi ng a calculation on the results. It is elementary that claim construction begins with, and remains focused on, the language of the claims. Innova/Pure Water, Inc. v. Sa fari Water Filtration Sys., Inc. , 381 F.3d 1111, 1116 (Fed. Cir. 2004). As our recent en banc decision in Phillips v. AWH Corp. reaffirmed, the words of a claim are gener ally given their or dinary and customary

04-1414 7meaning, which is the meaning the term would have to a person of ordinary skill in the art at the time of the invention. 415 F.3d 1303, 1312-13 (Fed. Cir. 2005) (en banc) (citing Innova , 381 F.3d at 1116). Such a person is deemed to read the claim term in the context of the entire paten t, including the other claims and the written description. Id. at 1313. Patent claims s hould also be construed in light of the prosecution history, which, like the patent itself, has been designat ed as part of the “int rinsic evidence.” Id. at 1317. Extrinsic evidence, such as expert testimony, may be useful in claim construction, but it should be considered in the context of the intrinsic evidence. Id. at 1318-19. In this case, the plain language of the clai ms gives no indication that the amount of phosphorous-containing acid in the claimed invention is a chemical equivalent amount. The claim language clearly refers to the “amount” of phos phorous-containing acid that is “present” in t he “concentrated phosphorus fertilizer.” 2 Furthermore, the written description contains no discussion at all of ‘chemical equivalents’ or any hint that the amount of phosphorous-containi ng acid recited in the claims is expressed as a chemical equivalent amount instead of the am ount actually present in the fertilizer. As for the prosecution history of the ’255 patent, Biagro relies on only one passage—a statement made by t he examiner during reexami nation that the phosphite solution of a prior art reference was an ex ample of a phosphorous acid solution. At most this shows that a person skilled in the art might refer to a phosphite solution as a

2 As often happens in claims having an absence of useful punctuation, the addition of new language creates ambiguities. In this case, it is unclear whether the “wherein” phrase modifies “[a] concentra ted phosphorous fertilizer,” or “a buffered composition,” or “a fully sol ubilized use-dilution fertilizer.” For purposes of the result, it does not matter.

04-1414 8phosphorous acid solution when the phosphite solu tion, like the accused product in this case, was formed from phosphorous acid. But we do not conclude from this one statement that one skilled in the art w ould interpret claim language concerning the amount of phosphorous acid r equired to be “present” in the fertilizer to mean the amount of phosphorous acid that was used to make the fertilizer, i.e., the chemical equivalent amount. The prosecut ion history, like the patent it self, is devoid of the term chemical equivalent or any reference to t he use of representativ e amounts to describe the composition of the fert ilizers claimed in the patent. Biagro also cites the prosecution histor y of U.S. Patent No. 6,113,665 (“the ’665 patent”), which is a continuat ion of the ’255 patent and was prosecuted during the same timeframe as the reexamination of the ’255 patent. In remarks accompanying two amendments that added limitati ons on the amount of phosphor ous-containing acid or salt present in the claimed fertilizer, the app licant’s attorney referred to the amount of phosphorous acid “in” examples 1 and 9 of the written description. According to Biagro, these amounts were chemical equivalent amounts because the fertilizers produced in those examples do not actua lly contain phosphorous acid. As the trial court noted, however, there is nothing in the prosecution history of the ’ 665 patent to explain how the figures were obtained or to indicate that the examiner underst ood the applicant was referring to chemical equivalent amounts. Whatever the attorney’s statements were intended to mean, they do not alter the ordinary meaning of the claim language, i.e., that the amount of phosphorous-c ontaining acid is the amount actually present in the fertilizer.

04-1414 9In making its arguments, Biagr o relies heavily on extrinsic evidence in the form of expert declarations explaining fertilizer labeling guidelines and standards. This evidence, according to Biagro, shows that those skilled in the ar t understand that the amounts of plant nutrients in fertilizer products are frequently expressed as ‘chemical equivalents.’ The primary example is a fe rtilizer labeling convention, known as the ‘guaranteed analysis,’ which indicates t he guaranteed amount of nitrogen, phosphorus, and potassium in the fertilizer product. The phosphorus content is expressed not in its elemental form (P), but as phosphorus pentoxide (P 2 O 5 ), regardless of whether the fertilizer actually contains any phosphorus pentoxide. Thus t he amount of phosphorus pentoxide listed on the label is a chemical equivalent amount deriv ed from the actual chemical composition of the fertilizer. Bi agro also cites California fertilizer labeling guidelines that refer to fertilizer products as “containing” phosphorous acid when in fact they were only derived from phosphorous acid. In Biagro’s view, this evidence shows that a person skilled in the art would underst and the claims to refer to a chemical equivalent amount of phosphorous-containing acid , and therefore we should accept this interpretation as the ordinary and cust omary meaning of the claim language. However, even if we agree that t he labeling convention and guidelines demonstrate that those skill ed in the art are familiar with the use of ‘chemical equivalents,’ the problem is t hat Biagro cannot tie its extrin sic evidence to the patent or the claim language. Nothing in the patent or prosecution history indicates that labeling standards are relevant to the claimed fe rtilizer, and nothing in Biagro’s extrinsic evidence suggests that a per son skilled in the art of fertilizer form ulation would

04-1414 10necessarily use a chemical equivalent to express the amount of phosphorous acid in a fertilizer that does not actually contain phosphorous acid. We are also unpersuaded by Bi agro’s argument that GrowMore’s expert took an inconsistent position on behalf of a differ ent defendant in another patent infringement suit brought by Biagro. In that case, t he expert described a prio r art fertilizer as containing 13% phosphorous acid, which was ultimately shown to be a chemical equivalent amount. We agree with the trial c ourt that it appears t he expert was simply relying on product materials shown to hi m and was not aware that the 13% had been arrived at through a ‘chemical equivalent’ analysis.
2. Biagro’s second theory is that the trial court erred in cons truing the amount of “phosphorous-containing acid or salt” in the claim language as an aggregate amount. The claim language calls for “at least one phosphorous-containing acid or salt thereof . . . wherein said phosphorous-containing acid or salt thereof is present in an amount of about 30 to about 40 weight percent.” Biagro argues that t he limitation is met so long as one acid or salt is present in the claimed amount, ev en if the fertilizer contains other acids or salts. Under the tr ial court’s claim construction, as advocated by Grow More, a fertilizer containing more than one acid or salt would satisfy the limitation only if the aggregate amount of acids or salts falls within the claimed range. The phrase “at least one” in patent claims ty pically is construed to mean “one or more.” Therefore, Biagro contends, the cl aim language allows for aggregation of acids or salts but does not require i t. The trial court, however, concluded that both the written description and prosecution history require t he aggregate amount of acid s or salts to be

04-1414 11within the claimed range, and we agree. First, it is apparent from the written description that all phosphorous-containing acids or salts in the fertilizer serve the same purpose such that the total amount of such acids or salts is important. More significantly, during reexamination the patentee dist inguished the invention over prior art by emphasizing that the claimed fertilizer “must be concentrated ” and that the “concentration has now been specified as an amount of about 30 to about 40 weight percent.” If a fertilizer contains more than one phosphorous-containing ac id or salt, the concentration is based on the total amount of such acids or salts, not just one acid or salt. In view of the patentee’s emphasis on the concentration of phosphorous-containing acids or salts, the trial court correctly construed the claim to require an aggregate amount of such acids or salts to be between about 30 and about 40 weight percent. C. Infringement 1. Literal Infringement Having affirmed the trial court’s claim constr uction, we also affirm the trial court’s grant of summary judgment of no literal infringement with res pect to both of the theories presented by Biagro. Firs t, because we have rejected Biagro’s chemical equivalent claim construction argument, there can be no literal infringement based on the amount of phosphorous acid, an ingredient used to make the accused fertilizer but not actually present in the final product. Biagro’s second literal infri ngement theory is that potassi um phosphite is present in the accused product in an amount of 40. 3%, which Biagro alleges is within the claimed range of “about 30 to about 40 weight percent.” The correct claim construction, however, requires the aggregate amount of phosphites to be wit hin the claimed range.

04-1414 12Because the accused product contains tw o phosphites, resulting in an aggregate phosphite content of at least 59.3%, clear ly outside the claimed range, no reasonable jury could find literal infringement based on the presence of phosphites. 2. Infringement Under t he Doctrine of Equivalents Biagro also asserts that Grow More’s fe rtilizer infringes the claims of the ’255 patent under the doctrine of equivalents because the aggregate phosphite concentration of between 59% and 62% is equivalent to t he claimed concentration of about 30 to about 40 weight percent. The tr ial court did not reach the issue in those terms in its initial summary judgment orderbecause it held that, under Festo I , prosecution history estoppel acted as a complete bar to a claim of infringement by equivalents. Later, after the Supreme Court’s Festo II decision and this court’s Festo III decision on remand, the trial court reconsidered its summary judgm ent ruling, but still held that Biagro was barred from asserting the doctrine of equi valents because it failed to rebut the Festo presumption. A narrowing amendment made for a substant ial reason relating to patentability gives rise to a presumpt ion that the patentee has surrendered all subject matter between the original claim limitati on and the amended clai m limitation. Festo III , 344 F.3d at 1367. If the narrowing amendment was the addition of a new claim limitation, as in the case before us, equival ents are presumptively not ava ilable with respect to that limitation. Honeywell Int’l Inc. v. Hamilton Sundstrand Corp. , 370 F.3d 1131, 1141 (Fed. Cir. 2004). A patentee may rebut the presumption of surrender by s howing that at the time of the amendment one skilled in the art could not reasonably be expected to have drafted

04-1414 13a claim that would have literally encompassed the alleged equivalent. Festo II , 535 U.S. at 741. The Supreme Court identified three ways in which the patentee may overcome the presumption. The patent ee may show that the alleged equivalent would have been unforeseeable at the time of the amendment, that the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question, or that there was “some other reas on” that the patentee coul d not reasonably have been expected to have described the alleged equivalent. Id. at 740-41. As an initial matter, we reject Biagro’ s argument that at the summary judgment stage the burden is on Grow More to present undisputed facts showing that Biagro cannot rebut the Festo presumption. The Supreme C ourt made clear t hat the patentee bears the burden of rebutting the presumption of surrender. Id. at 740. Furthermore, the determination of whether the presumption has been rebutt ed is a question of law. Festo III , 344 F.3d at 1368. Although in some si tuations there may be underlying factual issues, id. at 1368 n.3, neither of Biagro’s rebuttal arguments involves disputed facts, as will be explained below. We begin by examining the amendment that was made to the claims of the ’255 patent. During reexamination, the patentee made a narrowing amendment to all of the independent claims by adding the claim limitat ion “wherein said phosphorous-containing acid or salt thereof is present in an am ount of about 30 to about 40 weight percent.” The amendment was made to overcome a prio r art obviousness rejection based on a reference describing a fertilizer that was buffe red only when diluted. To distinguish the claims over the prior art reference, the patentee explained to the examiner that the fertilizer must be concentrated and that the amendment specifi ed a range for the

04-1414 14concentration. Therefore the narro wing amendment was made for a reason substantially related to patentability, and Biagro has presumptively surrendered any equivalents with respect to the amount of phos phorous-containing acid or salt present in the fertilizer. Biagro first attempts to rebut the pres umption of surrender by arguing that the rationale underlying the amendm ent was no more than tangentially related to the asserted equivalent. As we explained in Festo III , whether the patentee has overcome the presumption on this ground is determined by the court on the basis of the public record. Id. at 1369-70. In this case , it is clear from the pr osecution history that the reason for adding the range limitati on was to overcome a prior art fertilizer that was not concentrated. Here the alleged equivalent is a fertilizerwith a phosphite concentration of nearly 60%. Because both the reason for the amendm ent and the asserted equivalent relate to the concentration of the fertilizer, we affirm the trial court’s conclusion that Biagro has not shown that the rational e underlying the amendment was merely tangential to the accused equivalent. We disagree with Biagro that this case is analogous to Insituform Technologies, Inc. v. Cat Contracting, Inc. , 385 F.3d 1360 (Fed. Cir. 2004). That case involved a method for impregnating a tube liner with a resin by moving a single vacuum cup to multiple points along the tube liner. The a ccused process used multiple vacuum cups, and the patentee asserted that the multiple-c up process was equivalent to the singlecup process. The original cl aim did not specify the number orlocation of vacuum cups. During prosecution, the patent ee incorporated several limit ations from dependent claims

04-1414 15into independent claim 1. The prosecution history showed that the reason for the amendment was to overcome a prior art proc ess that used a single vacuum source at the end of the tube liner dist ant from the resin source. Thus the reason for the amendment and the alleged equival ent involved different aspects of the invention—the location of the vacuum source relative to t he resin versus the number of vacuum cups. Id. at 1370. Accordingly, we concluded that the rationale underlying the amendment was tangential to the allegedly equivalent proc ess. In contrast, the reason for the amendment and the accused equiva lent in the case before us both relate to the concentration of the fertilizer. Biagro also argues that bec ause only the lower limit of the claimed range was necessary to distinguish over prior art, the reason for the amendment is merely tangential to an accused equival ent at the upper end of the range. In effect, Biagro is arguing that there was no reas on for adding an upper limit of 40%. Viewed from that perspective, the situation is analogous to the amendment in Festo that added the “magnetizable” limitation. The prosecution history re vealed no reason for the amendment, and therefore Festo could not show that the rationale underlying the amendment was only tangential to the accused nonmagnetizable equivalent. Festo III , 344 F.3d at 1371-72. Similarly, in this ca se, since the prosecution history shows no reason for adding an upper limit to the concentration range, Bi agro cannot claim that the rationale for the amendment is merely tangential. Biagro further argues t hat it can rebut the Festo presumption of surrender with “some other reason” that the patentee could not r easonably have been expected to have described the alleged equivalent when it na rrowed the claim. That “other” reason

04-1414 16is that the patentee allegedl y understood the claim language to refer to a chemical equivalent amount of phosphorous acid. We agree with the trial court that Biagro’s contention should be rejected as merely an attempt to reargue the claim construction issue. Moreover, we fail to see how the patentee’s supposed inability to draft claims to cover chemical equivalent amounts relates to Biagro’s equivalence argument, which is that the approximately 60% c oncentration of phosphite actua lly present in the accused product is equivalent to the claimed 30-40% concentration. For the reasons discussed, we affirm the tr ial court’s holding t hat Biagro has not rebutted the presumption of surrender and that prosecution history estoppel bars Biagro from asserting infringement underthe doctrine of equivalents.

CONCLUSION The judgment of the trial court is in all respects AFFIRMED

.

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