  United States Court of Appeals
      for the Federal Circuit
                ______________________

 PHARMA TECH SOLUTIONS, INC., DECISION IT
                  CORP.,
            Plaintiffs-Appellants

                           v.

  LIFESCAN, INC., LIFESCAN SCOTLAND, LTD.,
         JOHNSON AND JOHNSON,
              Defendants-Appellees
             ______________________

                      2019-1163
                ______________________

    Appeal from the United States District Court for the
District of Nevada in No. 2:16-cv-00564-RFB-PAL, Judge
Richard F. Boulware, II.
                 ______________________

              Decided: November 22, 2019
                ______________________

   JOHN J. SHAEFFER, Fox Rothschild LLP, Los Angeles,
CA, argued for plaintiffs-appellants. Also represented by
JEFFREY H. GRANT; WILLIAM A. RUDY, Denver, CO.

    EUGENE M. GELERNTER, Patterson Belknap Webb &
Tyler LLP, New York, NY, argued for defendants-appel-
lees. Also represented by GREGORY DISKANT; CHARLES
DAVISON HOFFMANN, SEAN REEVES MARSHALL, Hoffmann
Marshall Strong LLP, New York, NY.
                ______________________
2                   PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




    Before MOORE, REYNA, and STOLL, Circuit Judges.
STOLL, Circuit Judge.
    This is an appeal from the district court’s summary
judgment of noninfringement under the doctrine of equiv-
alents. Because prosecution history estoppel bars the
claims for infringement under the doctrine of equivalents,
we affirm.
                        BACKGROUND
                              I
    Pharma Tech Solutions, Inc. sued LifeScan, Inc. for in-
fringement of its U.S. Patent Nos. 6,153,069 and 6,413,411,
which concern blood glucose monitoring systems for home
use by individuals with diabetes. To test blood glucose, an
individual typically draws blood by pricking a finger, plac-
ing the blood on the end of a test strip, and placing the test
strip into a meter. The test strip contains a pair of elec-
trodes, including a working electrode and a second elec-
trode. The working electrode is coated with an enzyme that
oxidizes glucose in the blood sample. Following an incuba-
tion period, the meter (1) applies a known electric potential
across the electrodes, creating a diffusion limiting electric
current (referred to as the “Cottrell current”) through the
sample; and (2) measures Cottrell current. A proportional
relationship exists between the measured current and
blood glucose concentration. Based on this proportional re-
lationship, a microprocessor in the meter converts the
measured electric current to a blood glucose level and then
reports the blood glucose level to the user.
    The shared specification of Pharma Tech’s ’069 and
’411 patents states that the claimed inventions improve on
these prior art blood glucose monitoring systems by “elim-
inat[ing] several of the critical operator depend[e]nt varia-
bles that adversely affect the accuracy and reliability” of
these systems. ’069 patent col. 4 l. 66–col. 5 l. 3. The
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                   3



specification explains that the invention accomplishes this
objective by performing multiple Cottrell current measure-
ments and comparing the results. “In a system that is op-
erating correctly, the results should agree within
reasonable limits.” Id. at col. 4 ll. 51–52. Results outside
of a prescribed percentage of each other, however, gener-
ally indicate a system error, and the system will alert the
user of a potential measurement error.
    With emphasis added to highlight the claim limitation
at issue on appeal, illustrative claim 1 of the ’069 patent
recites:
    1. An apparatus for measuring compounds in a
    sample fluid, comprising:
    a) a housing        having    an   access   opening
    therethrough;
    b) a sample cell receivable into said access opening
    of said housing, said sample cell being composed of;
      (i) a first electrode which acts as a working elec-
      trode;
      (ii) a second electrode which acts to fix the sys-
      tem potential and provide opposing current flow
      with respect to said first electrode, said second
      electrode being made of the same electrically
      conducting material as said first electrode, and
      being operatively associated with said first elec-
      trode, the ratio of the surface area of said second
      electrode to the surface area of said first elec-
      trode being 1:1 or less;
      (iii) at least one non-conducting layer member
      having an opening therethrough, said at least
      one non-conducting layer member being dis-
      posed in contact with at least one of said first
      and second electrodes and being sealed against
      at least one of said first and second electrodes to
4                     PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




       form a known electrode area within said opening
       such that said opening forms a well to receive
       the sample fluid and to allow a user of said ap-
       paratus to place the sample fluid in said known
       electrode area in contact with said first electrode
       and said second electrode;
    c) means for applying an electrical potential to both
    said first electrode and said second electrode;
    d) means for creating an electrical circuit between
    said first electrode and said second electrode
    through the sample fluid;
    e) means for measuring a first Cottrell current
    reading through the sample fluid at a first prede-
    termined time after the electrical potential is ap-
    plied and for obtaining at least one additional
    Cottrell current reading through the sample fluid,
    the at least one additional Cottrell current reading
    occurring at a second predetermined time following
    the first predetermined time;
    f) microprocessor means for converting the first Cot-
    trell current reading into a first analyte concentra-
    tion measurement using a calibration slope and an
    intercept specific for the first Cottrell current meas-
    urement, for converting the at least one additional
    Cottrell current reading into an additional analyte
    concentration using a calibration slope and an in-
    tercept specific for the at least one additional Cot-
    trell current measurement, and for comparing the
    first analyte concentration measurement with the at
    least one additional concentration measurement to
    confirm that they are within a prescribed percent-
    age of each other; and
    g) means for visually displaying the results of said
    analyte concentration measurements.
Id. at col. 13 ll. 10–61.
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                   5



                              II
    The product accused of infringing under the doctrine of
equivalents is LifeScan’s OneTouch® Ultra® system, a
blood glucose meter for home use. When blood is detected
on a test strip inserted into LifeScan’s meter, the meter
measures current from two working electrodes during a
five-second countdown period. LifeScan’s meter obtains fi-
nal current measurements from the first and second work-
ing electrodes at “5 seconds + 40 milliseconds (±25ms) after
the measurement period begins” and “5 seconds + 340 ms
(±25ms) after the measurement period begins.” J.A. 57.
    LifeScan’s meter then conducts a “Current Difference
Test” to ensure that the difference between the recorded
currents is within a defined limit. J.A. 57. “If the Current
Difference Test passes, then the total final current (com-
bining both working electrodes) is calculated.” J.A. 58. “[A]
single glucose result is calculated from the total final cur-
rent using a strip slope and intercept based on the strip’s
calibration code.” J.A. 58.
    It is undisputed that LifeScan’s meters neither convert
multiple Cottrell current readings to analyte concentration
measurements nor compare multiple analyte concentra-
tion measurements. Pharma Tech agrees that the accused
products therefore do not literally infringe the claim. But
Pharma Tech asserts that “an analyte measurement can be
expressed as a current at a given time or as a concentra-
tion” and, thus, the accused device infringes under the doc-
trine of equivalents. Appellant’s Br. 40.
                             III
     Because this appeal involves prosecution history estop-
pel, a discussion of the relevant prosecution history is help-
ful. Pharma Tech agrees that any prosecution history
estoppel determined to apply to the ’069 patent extends to
the related ’411 patent, so we focus on the prosecution his-
tory of the ’069 patent.
6                     PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




    As originally filed, claim 4 of the patent application
that ultimately issued as the ’069 patent (application claim
4) read as follows:
    4. An apparatus for measuring compounds in a
    sample fluid, comprising
    a) a housing        having    an    access    opening
    therethrough[,]
    b) a sample cell receivable into said access opening
    of said housing, said sample cell being composed of
      a first electrode which acts as a working elec-
      trode,
      a second electrode which acts to fix the system
      potential and provide opposing current flow with
      respect to said first electrode, said second elec-
      trode being of substantially the same size as said
      first electrode and being made of the same elec-
      trically conducting material as said first elec-
      trode, said second electrode being operatively
      associated with said first electrode,
      at least one non-conducting layer member hav-
      ing an opening therethrough said layer member
      being disposed in contact with at least one of
      said electrodes and said layer member being
      sealed against at least one of said first and sec-
      ond electrode to form a known electrode area
      within said opening such that said opening
      forms a well to receive said sample fluid and to
      place said fluid in said known electrode area in
      contact with said first electrode and said second
      electrode,
    (c) means for applying an electrical potential to
    said first electrode and said second electrode,
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                    7



    (d) means for creating an electrical circuit between
    said first electrode and said second electrode
    through said sample,
    (e) means for measuring Cottrell current through
    said sample and
    (f) means for visually displaying results of said
    measurement.
J.A. 220–21. As Pharma Tech’s expert acknowledged, this
originally presented claim was “broad enough to essen-
tially cover any test strip with two working electrodes.”
J.A. 698.
     In a first office action, the examiner rejected the inven-
tors’ pending claims in view of U.S. Patent No. 5,385,846
(Kuhn), U.S. Patent No. 5,288,636 (Pollmann), and U.S.
Patent No. 5,108,564 (Szuminsky). The inventors’ October
1997 response to the examiner’s office action amended ap-
plication claim 4 (which later issued as ’069 patent claim
1). Among other things, the claim was amended to require:
(1) obtaining at least two Cottrell current readings; (2) con-
verting the plurality of Cottrell current readings to analyte
concentration measurements; and (3) linearly comparing
the plurality of analyte concentration measurements:
    e) means for measuring a first Cottrell current
    reading though said sample at a first predeter-
    mined time after said electrical potential is applied
    and for obtaining at least one additional Cottrell
    current reading through said sample, said at least
    one additional Cottrell current reading occurring
    at a second predetermined time following said first
    predetermined time,
    f) means for converting said first Cottrell current
    reading into a first analyte concentration measure-
    ment, and for converting said at least one addi-
    tional Cottrell current reading into an additional
    analyte concentration measurement, and for
8                  PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




    linearly comparing said first analyte concentration
    measurement to said additional analyte concentra-
    tion measurement[.]
J.A. 303 (underlined text added by amendment).
     In the remarks accompanying the October 1997
amendment, the inventors emphasized the new claim lan-
guage and distinguished the asserted prior art based
thereon. For example, the inventors argued, “Kuhn is not
applicable to claims 4 or 66 as now amended, in that ob-
taining a plurality of readings by taking repeated measure-
ments is not the same as the multiple readings now
claimed, wherein those readings are converted to analyte
concentration and then linearly compared to one another.”
J.A. 307 (emphasis added). The inventors distinguished
Pollmann and Szuminsky on the same basis, asserting:
“Pollmann likewise does not suggest the present claimed
means for comparing the concentration derived from the
first measurement and at least one additional concentra-
tion derived from an additional measurement to verify the
result.” J.A. 307–08 (emphasis added); see also J.A. 308
(“Claims 66–69 all include the additional multiple meas-
urement limitation, wherein the multiple measurements
are used to verify the result by comparing concentrations
determined at different times during the measurement.” 1
(emphasis added)).
   In a second office action, the examiner rejected the
pending claims as anticipated by U.S. Patent No. 5,508,171



    1 The October 1997 amendment amended application
claim 66 to depend from application claim 4. Claims 67–
69, which issued as independent claims 4–6 of the ’069 pa-
tent, were amended to recite limitations requiring obtain-
ing a plurality of current readings and comparing analyte
concentrations derived from said current readings.
J.A. 304–06.
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                  9



(Walling) and as obvious over Walling in view of Szumin-
sky or U.S. Patent No. 5,243,516 (White). J.A. 359–61. The
examiner explained that Walling discloses “means for ap-
plying an electrical potential between the electrodes and
means for measuring a resulting diffusion limiting current
at multiple times.” J.A. 360 (citing Walling col. 3 l. 29,
col. 8 l. 55–col. 12 l. 55). Noting that Szuminsky and White
each disclose a microprocessor to take measurements in a
sensor similar to that of Walling, the examiner concluded
that “[i]t would have been obvious for Walling to adopt a
microprocessor in view of Sz[u]minsky or White.” J.A. 361.
The examiner further concluded that the applicants’ “line-
arly comparing” limitation did not change the obviousness
analysis, because “any microprocessor is capable of carry-
ing out that function.” J.A. 361.
     In response, the inventors again highlighted the “con-
verting” and “comparing” claim language added by the Oc-
tober 1997 amendment. For example, the inventors
emphasized that “Walling et al and Szuminsky et al do not
even disclose taking multiple analyte concentration meas-
urements and comparing such to confirm proper operation
of a measuring system.” J.A. 378. Similarly, to distinguish
White, the inventors argued that “[i]n contrast to the teach-
ings in White, the present invention compares analyte con-
centration readings at different times.” J.A. 378.
   The examiner again rejected the claims as obvious over
Walling in view of White in a third office action. Following
an examiner interview, the inventors filed another re-
sponse in which they repeatedly distinguished the prior art
based on the “converting” and “comparing” limitations.
The inventors asserted:
    the present invention is directed to a system which
    takes two different Cottrell current readings, con-
    verts them to two different analyte concentration
    measurements, and then compares the two analyte
    concentration measurements to each other to
10                   PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




     confirm that they are within a prescribed percent-
     age of each other. That operation in the present
     invention is neither taught nor suggested by Wall-
     ing et al or White (’516), or any combination
     thereof.
J.A. 397–98. The inventors then distinguished Walling on
the basis that “Walling et al does not convert two different
Cottrell current readings to first and second analyte con-
centration measurements, and then compare the first and
second analyte concentration measurements to each other,
as in the present invention.” J.A. 398. Rather, they as-
serted, Walling “utilize[s] the multiple [current] measure-
ments together to determine a proper analyte
concentration.” J.A. 398. Turning to White, the inventors
asserted that “White (’516) discloses an operation in which
Cottrell current measurements at two different times are
taken and a ratio of the measured Cottrell currents [is]
evaluated.” J.A. 398. The inventors explained that the
claimed “converting” limitation and the claimed “compar-
ing” limitation each provided a basis to distinguish “the
present invention” over White:
     First, in the present invention the two different
     Cottrell current readings are converted into first
     and second analyte concentration measurements.
     Further, in the present invention the first and sec-
     ond analyte concentration measurements based on
     the first and second Cottrell current readings are
     compared to each other to confirm that they are
     within a prescribed percentage of each other.
J.A. 398. Continuing, the inventors emphasized that be-
cause neither Walling nor White “disclose[s] or suggest[s]
comparing first and second analyte concentration measure-
ments based on first and second Cottrell current readings
to each other,” the combination of White and Walling can-
not render the claims obvious. J.A. 399.
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                11



     In response, the examiner issued a notice of allowabil-
ity, and the ’069 patent issued. The ’411 patent, which is a
continuation of the ’069 patent, issued subsequently.
                             IV
    After Pharma Tech filed a complaint for infringement
of the ’069 and ’411 patents, LifeScan moved to dismiss
Pharma Tech’s complaint based on failure to state a claim
upon which relief could be granted for both literal and
equivalent infringement.       The district court denied
LifeScan’s motion, allowed Pharma Tech to amend its com-
plaint, granted expedited discovery limited to infringement
of the “converting” and “comparing” limitations, and per-
mitted LifeScan to file an early motion for summary judg-
ment. For its doctrine of equivalents infringement claims,
Pharma Tech’s amended complaint identified the relevant
equivalent as “the functionality of a system that
(a) measures current at two different times, (b) compares
the current[s] to ensure they are within a prescribed per-
centage and (c) converts the current readings into a glucose
concentration.” J.A. 1047–48.
    After Pharma Tech dismissed its literal infringement
allegations, LifeScan filed a motion for summary judgment
of no infringement under the doctrine of equivalents.
LifeScan asserted that argument-based and amendment-
based prosecution history estoppel barred Pharma Tech’s
doctrine of equivalents infringement theory. Specifically,
LifeScan asserted that when the inventors amended their
claims to require conversion of Cottrell current readings to
analyte concentration measurements and subsequent com-
parison of those analyte concentration measurements, they
surrendered any claim scope covering systems and meth-
ods that do not compare analyte concentration measure-
ments.     In addition, LifeScan maintained that the
inventors’ arguments distinguishing the prior art consti-
tuted clear and unambiguous disclaimers of meters that do
not perform the claimed conversion and comparison steps.
12                  PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




Pharma Tech opposed summary judgment, asserting that
its October 1997 amendment of the claims to include the
“conversion” and “comparison” steps was tangential to the
real purpose of the amendment, which was to require a lin-
ear comparison of multiple measurements.
    The district court held that amendment-based prosecu-
tion history estoppel barred Pharma Tech’s claims of in-
fringement under the doctrine of equivalents. The court
reasoned that LifeScan’s accused system falls within the
claim scope surrendered by the inventors during prosecu-
tion of the ’069 patent. In so ruling, the district court con-
cluded that the tangentiality exception did not apply
because the inventors’ remarks during prosecution indi-
cated that “comparison of analyte concentration measure-
ments was, at a minimum, a significant aspect of the
[October 1997] amendment.” Pharma Tech Sols. Inc. v.
LifeScan Inc., 348 F. Supp. 3d 1076, 1084 (D. Nev. 2018).
The district court further held that argument-based estop-
pel likewise barred Pharma Tech’s claims, noting that the
inventors “consistently relied on the comparison of two an-
alyte concentration measurements as a distinguishing fea-
ture of [their] claims.” Id. Accordingly, the district court
granted LifeScan’s motion for summary judgment.
   Pharma Tech appeals.           We have jurisdiction under
28 U.S.C. § 1295(a)(1).
                        DISCUSSION
                              I
    We apply the standard of review of the regional circuit
in reviewing a grant of summary judgment. Enfish, LLC
v. Microsoft Corp., 822 F.3d 1327, 1334 (Fed. Cir. 2016).
The Ninth Circuit reviews a district court’s grant of sum-
mary judgment de novo. Forester v. Chertoff, 500 F.3d 920,
923 (9th Cir. 2007). “Viewing the evidence in the light most
favorable to the non-moving party, we must decide whether
any genuine issues of material fact exist and whether the
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                 13



district court correctly applied relevant substantive law.”
Id. “Whether prosecution history estoppel applies, and
thus whether the doctrine of equivalents is available for a
particular claim limitation, is a question of law reviewed
de novo.” Spectrum Pharm., Inc. v. Sandoz Inc., 802 F.3d
1326, 1337 (Fed. Cir. 2015).
                             II
    “Prosecution history estoppel applies as part of an in-
fringement analysis to prevent a patentee from using the
doctrine of equivalents to recapture subject matter surren-
dered from the literal scope of a claim during prosecution.”
Trading Techs. Int’l, Inc. v. Open E Cry, LLC, 728 F.3d
1309, 1322 (Fed. Cir. 2013). Prosecution history estoppel
can occur in two ways: “either (1) by making a narrowing
amendment to the claim (‘amendment-based estoppel’) or
(2) by surrendering claim scope through argument to the
patent examiner (‘argument-based estoppel’).” Conoco,
Inc. v. Energy & Envtl. Int’l, L.C., 460 F.3d 1349, 1363
(Fed. Cir. 2006).
     With respect to amendment-based prosecution history
estoppel, the Supreme Court has recognized that a “pa-
tentee’s decision to narrow his claims through amendment
may be presumed to be a general disclaimer of the territory
between the original claim and the amended claim.” Festo
Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S.
722, 740 (2002). The presumption may be overcome if the
patentee can show the applicability of one of several excep-
tions identified by the Supreme Court: (1) the equivalent
was “unforeseeable at the time of the application”; (2) “the
rationale underlying the amendment may bear no more
than a tangential relation to the equivalent in question”; or
(3) “there may be some other reason suggesting that the
patentee could not reasonably be expected to have de-
scribed the insubstantial substitute in question.” Id.
at 740–41.
14                  PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




    Pharma Tech does not dispute that the October 1997
amendment was narrowing, and relies on one of these ex-
ceptions on appeal: that the rationale of its amendment
bore no more than a tangential relation to the equivalent
in question. “The tangential relation inquiry ‘focuses on
the patentee’s objectively apparent reason for the narrow-
ing amendment,’ which ‘should be discernible from the
prosecution history record.’” Integrated Tech. Corp. v. Ru-
dolph Techs., Inc., 734 F.3d 1352, 1358 (Fed. Cir. 2013)
(quoting Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki
Co., 344 F.3d 1359, 1369 (Fed. Cir. 2003)).
    Turning to argument-based prosecution history estop-
pel, “the prosecution history must evince a clear and un-
mistakable surrender of subject matter.” Conoco, 460 F.3d
at 1364 (quoting Deering Precision Instruments, L.L.C. v.
Vector Distribution Sys., Inc., 347 F.3d 1314, 1326 (Fed.
Cir. 2003)). We have explained that “[c]lear assertions
made during prosecution in support of patentability,
whether or not actually required to secure allowance of the
claim, may also create an estoppel . . . because [t]he rele-
vant inquiry is whether a competitor would reasonably be-
lieve that the applicant had surrendered the relevant
subject matter.” PODS, Inc. v. Porta Stor, Inc., 484 F.3d
1359, 1368 (Fed. Cir. 2007) (alterations in original) (cita-
tions omitted).
                            III
    We hold that amendment-based and argument-based
prosecution history estoppel bar Pharma Tech’s infringe-
ment claims under the doctrine of equivalents. Pharma
Tech’s asserted equivalent is within the territory that the
inventors surrendered during prosecution of the ’069 pa-
tent. Moreover, the inventors’ arguments accompanying
and following the October 1997 amendment clearly and un-
mistakably surrendered systems that do not convert Cot-
trell current readings to analyte concentration
measurements and compare those analyte concentration
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                 15



measurements. The inventors’ clear statements not only
establish argument-based estoppel, but also negate
Pharma Tech’s reliance on the tangential relation excep-
tion.
                              A
    Prior to the inventors’ October 1997 amendment, appli-
cation claim 4 was broad enough to cover any bioelectrical
blood glucose monitoring system. The October 1997
amendment narrowed the claims to systems that convert a
plurality of current readings to analyte concentration
measurements and compare said analyte concentration
measurements. The applicants thus presumptively sur-
rendered any bioelectrical blood glucose monitoring sys-
tems that do not convert a plurality of current readings into
analyte concentration measurements and compare the re-
sulting analyte concentration measurements. Pharma
Tech’s asserted equivalent—“the functionality of a system
that (a) measures current at two different times, (b) com-
pares the current[s] to ensure they are within a prescribed
percentage and (c) converts the current readings into a glu-
cose concentration”—falls squarely within the territory be-
tween the original claim and the amended claim.
J.A. 1047–48.
    Resolution of the amendment-based prosecution his-
tory estoppel issue turns on whether the inventors’ objec-
tively apparent rationale underlying the narrowing
amendment bore no more than a tangential relation to the
accused LifeScan systems. See Integrated Tech., 734 F.3d
at 1358. Resolution of the argument-based estoppel issue
turns on whether the prosecution history evinces a clear
and unmistakable surrender of systems that do not convert
and compare analyte concentration measurements. See
Conoco, 460 F.3d at 1364. Here, the inventors clearly and
unambiguously distinguished their invention over the
prior art based on the converting and comparing limita-
tions added by the October 1997 amendment. We thus
16                  PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




agree with the district court that the inventors’ remarks
accompanying the October 1997 amendment make clear
that the amendment was made to achieve patentability—
and for reasons more than tangentially related to the
equivalent at issue. The objectively apparent reason for
the October 1997 amendment was to distinguish the inven-
tion over prior art systems that measured and displayed a
diffusion limiting current reading.
     The inventors consistently asserted that the Octo-
ber 1997 amendment overcame the prior art cited by the
examiner because the prior art did not compare analyte
concentration measurements derived (i.e., converted) from
diffusion limiting current readings. See, e.g., J.A. 307
(“Kuhn is not applicable to claims 4 or 66 as now amended,
in that obtaining a plurality of readings by taking repeated
measurements is not the same as the multiple readings
now claimed, wherein those readings are converted to ana-
lyte concentration and then linearly compared to one an-
other.” (emphasis added)); J.A. 307–08 (“Pollmann likewise
does not suggest the present claimed means for comparing
the concentration derived from the first measurement and
at least one additional concentration derived from an addi-
tional measurement to verify the result.”); J.A. 308
(“Claims 66–69 all include the additional multiple meas-
urement[s] . . . [that] are used to verify the result by com-
paring concentrations determined at different times during
the measurement. There is no teaching or suggestion in
Pollmann or Szuminsky to verify the measurement in the
way claimed in claim[s] 66–69.” (emphasis added)).
    The inventors’ arguments to the PTO throughout the
remainder of the prosecution history confirm our conclu-
sion. The inventors repeatedly and unequivocally de-
scribed “the present invention” as “a system which takes
two different Cottrell current readings, converts them to
two different analyte concentration measurements, and
then compares the two analyte concentration measure-
ments.” J.A. 397–98. And they continually argued that
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                 17



these features distinguished their invention over the prior
art. For example, with respect to White, the inventors ar-
gued: “In contrast to the teachings in White, the present in-
vention compares analyte concentration readings at
different times.” J.A. 378 (italics added). Distinguishing
Walling, the inventors similarly asserted, “Walling et al
does not convert two different Cottrell current readings to
first and second analyte concentration measurements, and
then compare the first and second analyte concentration
measurements to each other, as in the present invention.”
J.A. 398 (italics added). These same inventor statements
establish a clear and unmistakable surrender of subject
matter. The inventors’ remarks clearly and unambigu-
ously indicate their view that the sequence of performing
“converting” and “comparing” limitations was a distin-
guishing feature of “the present invention.” See J.A. 398
(“White (’516) differs from the present invention in the fol-
lowing respects. First, in the present invention the two dif-
ferent Cottrell current readings are converted into first and
second analyte concentration measurements. Further, in
the present invention the first and second analyte concen-
tration measurements . . . are compared to each other.”
(italics added)). Based on the inventors’ clear statements,
a competitor reviewing the prosecution history of the
’069 patent would reasonably believe that the inventors
had surrendered systems that do not convert diffusion lim-
iting current readings to analyte concentration measure-
ments and then compare the resulting analyte
concentration measurements. Accordingly, we also affirm
the district court’s determination that argument-based
prosecution history estoppel precludes Pharma Tech from
asserting infringement under the doctrine of equivalents.
    Citing Pioneer Magnetics, Inc. v. Micro Linear Corp.,
330 F.3d 1352, 1356 (Fed. Cir. 2003), Pharma Tech argues
that the “converting” and “comparing” claim limitations
were already disclosed in the prior art and, as such, these
limitations must have been added for reasons not related
18                  PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




to patentability. Appellant’s Br. 52. But Pioneer Magnetics
does not support this argument. In Pioneer Magnetics, we
held that the patentee’s narrowing amendment was “re-
lated to patentability” and “clearly not tangential” to the
asserted equivalent where the prior art contained the
equivalent. 330 F.3d at 1357. That the October 1997
amendment may have ceded more claim scope than neces-
sary to overcome prior art does not mean that the tangen-
tial relation exception applies here. Indeed, we have held
that “[t]he fact that the inventors may have thought after
the fact that they could have relied on other distinctions in
order to defend their claims is irrelevant” to discerning the
objective reason for their amendment. Int’l Rectifier
Corp. v. IXYS Corp., 515 F.3d 1353, 1359 (Fed. Cir. 2008)
(quoting Schwarz Pharma, Inc. v. Paddock Labs., Inc.,
504 F.3d 1371, 1377 (Fed. Cir. 2007)); see also Eli Lilly &
Co. v. Hospira, Inc., 933 F.3d 1320, 1332 (Fed. Cir. 2019)
(“Amendments are not construed to cede only that which is
necessary to overcome the prior art.” (citing Schwarz,
504 F.3d at 1377)). Accordingly, we reject Pharma Tech’s
argument based on Pioneer Magnetics.
                              B
    Finally, Pharma Tech analogizes the facts here to those
in cases where we held that amendment-based prosecution
history estoppel did not apply. For example, Pharma Tech
argues that Insituform Technologies, Inc. v. CAT Contract-
ing, Inc., 385 F.3d 1360 (Fed. Cir. 2004), controls the result
here. We disagree. In Insituform, the remarks accompa-
nying the patentee’s amendment did not emphasize or rely
on the added claim language to distinguish the prior art in
a manner relevant to the asserted equivalent. Id. at 1370.
This court held that Insituform’s amendment narrowing
the claim to a one-cup vacuum process located near a resin
source was merely tangentially related to an equivalent
multiple-cup vacuum process because the rationale under-
lying the amendment “was to avoid the need to use a large
compressor when the vacuum is created a significant
PHARMA TECH SOLS., INC. v. LIFESCAN, INC.                 19



distance from the resin source.” Id. (quoting Insituform
Techs., Inc. v. Cat Contracting, Inc., 161 F.3d 688, 692
(Fed. Cir. 1998)). Insituform noted “no indication in the
prosecution history of any relationship between the nar-
rowing amendment and a multiple cup process.” Id.
    Here, by contrast, the applicants’ October 1997 amend-
ment sought to avoid prior art systems that measured and
displayed diffusion limiting current. To distinguish their
claims from Kuhn, Pollmann, and Szuminsky, which meas-
ured and displayed diffusion limiting current, the inven-
tors amended their claims to require obtaining a plurality
of current readings, converting the current readings to an-
alyte concentration measurements, and comparing the an-
alyte concentration measurements to detect errors. The
inventors’ remarks accompanying the October 1997
amendment distinguished the prior art based on the newly
added sequential “converting” and “comparing” limita-
tions. It is undisputed that—like the prior art—LifeScan’s
meter does not convert diffusion limiting current readings
to analyte concentration measurements and then compare
analyte concentration measurements to one another to de-
tect errors.
    Recent cases from this court addressing amendment-
based prosecution history estoppel and the tangential rela-
tion exception are similarly distinguishable. In Eli Lilly,
for example, the patentee’s amendment narrowed the
claims in relevant part from requiring “an antifolate” to re-
quiring “permetrexed disodium.” 933 F.3d at 1325–26.
The equivalent at issue in Eli Lilly was permetrexed ditro-
methamine, a permetrexed salt functionally identical to
permetrexed disodium. Id. at 1327, 1336. We held that the
patentee’s amendment was merely tangentially related to
the equivalent at issue, because the prosecution history
“indicate[d] that the reason for the amendment was not to
cede other, functionally identical, permetrexed salts.” Id.
at 1331. Rather, “[t]he reason for Lilly’s amendment . . .
was to narrow original claim 2 to avoid Arsenyan, which
20                  PHARMA TECH SOLS., INC. v. LIFESCAN, INC.




only discloses treatments using methotrexate, a different
antifolate.” Id. Functionally equivalent permetrexed salts
were merely tangential to avoiding prior art disclosing an
antifolate other than permetrexed. Here, the comparison
of analyte concentration measurements was integral to the
inventors’ October 1997 amendment. The prosecution his-
tory indicates that throughout prosecution, the inventors
viewed the “converting” and “comparing” limitations as
necessary to overcome the prior art. See, e.g., J.A. 307,
377–78, 398–99. Accordingly, Eli Lilly is distinguishable.
    Likewise, in Ajinomoto, this court held that the ra-
tionale underlying the patentee’s amendment narrowing
the scope of the claimed DNA sequences to avoid the YfiK
prior art protein was unrelated to the asserted equiva-
lent—selecting from the codon-randomized sequences that
correspond to the YddG protein. Ajinomoto Co. v. Int’l
Trade Comm’n, 932 F.3d 1342, 1355 (Fed. Cir. 2019). Here,
by contrast, the rationale for the October 1997 amend-
ment—avoiding prior art that does not convert a plurality
of current readings or compare a plurality of analyte con-
centration measurements—directly relates to the accused
equivalent, a system which also does not convert a plural-
ity of current readings or compare a plurality of analyte
concentration measurements.
                       CONCLUSION
     We have considered Pharma Tech’s remaining argu-
ments, but do not find them persuasive. The district court
did not err in determining that prosecution history estop-
pel bars Pharma Tech from succeeding on its infringement
claims under the doctrine of equivalents. Accordingly, we
affirm the district court’s order granting LifeScan’s motion
for summary judgment.
                       AFFIRMED
