Rounding the Bend: Claim Construction and the Role of Extrinsic Evidence

by Dennis Crouch

Actelion Pharmaceuticals Ltd v. Mylan Pharmaceuticals Inc., No. 2022-1889 (Fed. Cir. Nov. 6, 2023) [decision]

The Federal Circuit’s bread-and-butter over the years has been claim constructions that often surprise or confuse district court judges. Part of the issue here is that most Federal Circuit judges have construed thousands of patents and are deeply immersed in the law of claim construction — while most district court judges see claim construction as a small part of a patent case, which itself is a small part of their overall docket. The other part of the issue, of course, is that no deference is given to the district court’s claim construction on appeal. The ensuing appeal then regularly turns out like that law school class where students seemed to provide really good answers in the Socratic game, but the professor could never resist tweaking — “almost right.”

The Actelion case involves a common situation where the patent claims include a measurement but do not state the level of precision, and the court is forced to decide whether values slightly outside the claimed range might be covered.

Actelion’s U.S. Patent Nos. 8,318,802 and 8,598,227 are directed to a new formulation of epoprostenol, a substance that naturally occurs in the human body and that is useful for treating cardiovascular diseases.  The claims appear directed to a product-by-process — a freeze dried powder (lyophilisate) formed from a solution that contains epoprostenol and that “has a pH of 13 or higher.” Mylan’s ANDA proposes a generic version that would have a pH made from a solution with pH slightly under 13.

The question for claim construction is whether the requirement of “13 or higher” pH encompasses something akin to a pH 12.6.  For abstract mathematicians, it is quite clear that 12.6 is less than 13 — the opposite of what is claimed. But, experimental scientists understand that a measurement of 12.6 might often be properly rounded to 13. The district court adopted Actelion’s proposed construction that “a pH of 13” includes values that round to 13, such as 12.5 and concluded that Mylan’s approach was infringing.  Mylan argued on appeal that the term requires an pH of “exactly” 13 — not values that are about or approximately 13.

The Federal Circuit opinion walked through various factors to help it understand the proper construction. As the court has held, the analysis begins with the claim language, as it is of primary importance. Additionally, “the specification is always highly relevant to the claim construction analysis” and is  often “the single best guide to the meaning of a disputed term.” Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005).

Claim Language: The court examined whether the language setting a lower limit of “13” precludes rounding or not. The claim is written as a whole number, rather than in decimal form. The district court noted that this involved “two significant figures’ without implying any higher level of precision.”  At oral arguments, the patentee’s counsel explained:

[The inventor] did not say 13.0, which is a figure that would have 10 times the greater precision, and certainly didn’t say ‘exactly 13’, which is not scientifically possible in the context of pH, because you’re talking about measurement of billions of ions in a liter of water of hydrogen ions and determining their concentration.

Oral args at 18:00. On the other side, in places the specification appeared to equate 13.0 to the whole number 13.

Lack of Approximation Terms: The court noted that the claim lacks words like “about” that would imply approximation and that are often included within patent claims. As the court explained, “Unlike other claim terms, the disputed claim term lacks approximation language like ‘about.'”

Nature of pH Measurements: The court considered whether pH values can be measured precisely or inherently require some margin of error. The court noted Actelion’s argument that “it is not practically possible to measure exact pH values” because it would require counting every hydrogen ion in solution.

Specification: The specification alternately uses approximation terms like “about” or lacks decimal points when describing pH values. For example, the specification states the pH is “preferably adjusted to about 12.5-13.5, most preferably 13.” This shows the inventor knew how to use “about” to imply approximation, but did not for the “13” value.  The statement also suggests that 12.5 is different from 13.  As the court summarized, “the specification is inconsistent, also describing pH values like ‘13.0’, ‘11.58’, and ’13’ without clear precision.”

Prosecution History: During patent prosecution, the patentee had distinguished its invention from a formulation with pH 12 — arguing that pH 13 exhibited substantially more stability. But the prosecution history did not compare pH 13 with values in between 12 and 13. As the court explained, the examiner “drew a distinction between the stability of a composition with a pH of 13 and that of 12” but this did not address whether pH 13 includes values rounding to 13.

With claim construction, the Federal Circuit has ruled that courts can quite often construe claims based solely upon intrinsic evidence. But, at times courts are permitted to go further and access extrinsic evidence like scientific texts.  Here, the Federal Circuit concluded that this is a case where extrinsic evidence  is necessary to understand how a skilled artisan would view the claim language in terms of pH precision and significant figures.  As the court explained, “this case is one where the proper claim construction cannot be reached without the aid of extrinsic evidence.” The appellate panel thus vacated the claim construction and infringement judgment and remanded for the district court to consider the extrinsic evidence like scientific textbooks and perhaps expert testimony in the process of reconsidering the claim construction.

The panel consisted of Circuit Judges Reyna, Stoll, and Stark. Circuit Judge Stoll authored the opinion.

= = =

This case highlights an issue that has led to claim construction disputes in numerous cases involving measurements and precision with billions of dollars turning on so-called rounding errors. The lack of clarity stems from applicants not specifying the precision or margin of error for claim terms either in the original application or during prosecution. This ambiguity could be avoided if the USPTO were to put the onus on patent applicants to identify the precision and error margin for any measurements recited in the claims. For example, the USPTO examiner could reject the claims as ambiguous based upon the broadest reasonable interpretation and require the applicant to clarify whether “a pH of 13” allows for values that round to 13 and if so, the acceptable variance (e.g. ± 0.1, ± 0.01 pH units).

Requiring patent applicants to explicitly identify the precision and error margin for measurements during prosecution would prevent the need for courts to resort to extrinsic evidence to resolve ambiguity that should have been addressed before issuance. This would increase certainty around claim scope and reduce unnecessary litigation.

What do you think, should the USPTO consider more ways to have applicants clarify claim term precision when filing and prosecuting applications involving numerical measurements?

37 thoughts on “Rounding the Bend: Claim Construction and the Role of Extrinsic Evidence

  1. 11

    A patent is a legal document but we are expected to construe it through the prism of a reader who is technical and skilled in the relevant art. The UK Supreme Court construes a claim by asking itself,what was the writer of the claim using the language of the claim to mean (to the hypothetical PHOSITA reader).

    A current English case (Heraeus vs First Light) the method claim to be construed stipulated that a glass bead should have a diameter “not bigger than” a particular tube. First Light’s bead was bigger. Nevertheless, their method was held to be a literal infringement because First Light’s variant on the claimed method “could have no material effect upon the way in which the invention worked”.

    I wonder what whether or not the lower court, upon remittal, will tell us whether, in the context of the case’s unique matrix of fact 12.5 is materially different from 13. As anon says at 8.1:

    “…it is a matter of understanding what the given precision means.”

    1. 11.2

      Not chemistry, nor physics (but much more basic), but let me know whether you think the legal fiction known as Person Having Ordinary Skill In The Arts would recognize a difference between:

      a) 13

      b) 13.00


      c) 13.0000000

      Hint: this understanding applies ‘math’ to any “Art” to which it is applied.

  2. 10

    It seems like the CAFC is calling for another “gotcha.”

    As it is, if the claim says “about” but there is nothing in the spec to expressly explain what that means, the claim is likely ambiguous and invalid. Personally, it seems to me that the CAFC could do better than that.

    Requiring applicants to expressly specify the precision, whenever a numerical value is specified, will mean that many applicants, ignorant of that, will file without specifying the precision, particularly pro se inventors. The more gotcha’s, the fewer valid patents, and patents have less value. The more gotchas in patent law, the less accessible the patent system is to the public, and the system becomes particularly inaccessible to those that are not well funded. It seems to me that if a patent is written with some degree of inconsistency, such as this patent, it should be just fine because that is just human.

    I think that the CAFC should do its job of interpreting claims in a manner that does not invalidate the claims in a manner that is consistent with its own caselaw, without belly-aching about it.

    1. 10.1

      For the record, the claims at issue here were not invalidated and the problematic element was the element that supposedly distinguished the alleged invention from the prior art.

      It’s seems less of a “gotcha” situation and more of a “follow best practices and build necessary support around critical elements” situation.

      There is nothing more that our patent system can (or should) do for “pro se” applicants beyond what it is doing now.

      1. 10.1.1

        You mean, other than:

        MPEP 707.07(j) State When Claims Are Allowable [R-11.2013]


        When, during the examination of a pro se application it becomes apparent to the examiner that there is patentable subject matter disclosed in the application, the examiner should draft one or more claims for the applicant and indicate in his or her action that such claims would be allowed if incorporated in the application by amendment.

        This practice will expedite prosecution and offer a service to individual inventors not represented by a registered patent attorney or agent. Although this practice may be desirable and is permissible in any case deemed appropriate by the examiner, it is especially useful in all cases where it is apparent that the applicant is unfamiliar with the proper preparation and prosecution of patent applications.

        or perhaps:

        1205.02 Appeal Brief Content [R-07.2022]

        An exception to the requirement that all the items specified in 37 CFR 41.37(c)(1) be included in the brief is made if the application or reexamination proceeding is being prosecuted by the appellant pro se, i.e., there is no attorney or agent of record, and the brief was neither prepared nor signed by a registered attorney or agent. The brief of a pro se appellant which does not contain all of the items specified in 37 CFR 41.37(c)(1) will be accepted as long as it substantially complies with the requirements of subparagraphs (i), (ii), (iv) and (v).

        or perhaps:

        713.01 General Policy, How Conducted [R-07.2022]

        During an interview with a pro se applicant (i.e., an applicant who is prosecuting his or her own case and is not familiar with Office procedure), the examiner may make suggestions that will advance the prosecution of this case; this lies wholly within the examiner’s discretion. Excessive time, however, should not be allowed for such interviews.

        among others…

  3. 9

    Below, MaxDrei comes close (albeit still misses) when he provides a non-US case with the comment of, “It’s physics rather than chemistry but that’s good because fact-finding is simpler.

    The issue here is NEITHER chemistry, nor physics, but rather something simpler still: the treatment of significant digits, and may well be viewed as being one of those “just math” things that turns around and is applied in a particular context.

    As I pointed out L O N G ago, the legal fiction known as Person Having Ordinary Skill In The Art (whether or not a judge figures this out or applies the legal/factual understanding appropriately), knows full well that:




    have different meanings.

    Another point here for the legally disadvantaged (and, as fairly typical, those tend to align with those denigrating patents), one can be broad without being ambiguous, and a patent application may well have a range of applications from broad to more precise without the “well, that’s got to be ambiguous” conclusory leap.

  4. 8

    Requiring recitation of a “precision” value will not solve this problem. If we recite “has a pH of 13 or higher, plus or minus 0.5,” that must be exactly the same as “has a pH of 12.5 or higher,” which will have the same problem. Said another way, people will just argue about the precision of the 0.5. That can reduce the numerical scope of the problem, perhaps, but there will still be the same arguments. This is best addressed by litigants being aware of these issues and wisely choosing claims and embodiments to pursue in litigation. The closer the embodiment is to the claimed number (or range), the more issues of precision and measurement (and claim scope and definiteness) there will be.

    1. 8.1

      Ron, I would tend to see that you are close – it is not a matter (per se) “of precision,” as much as it is a matter of understanding what the given precision means.

    2. 8.2

      Ron: “ This is best addressed by litigants being aware of these issues and wisely choosing claims and embodiments to pursue in litigation. The closer the embodiment is to the claimed number (or range), the more issues of precision and measurement (and claim scope and definiteness) there will be.”

      Exactly. In this case, the allegedly infringing product seems to have been as close to the prior art as it was to the claims.

      I suppose it’s possible to look at this case as a battle that was lost but which MIGHT have achieved the goal of convincing other competitors not to come any closer unless they want to spend a bunch of time and money in court.

  5. 7

    The critical nature of pH values, and the precision required, is most easily seen when looking at blood. Normal blood pH is between 7.2 and 7.4. If it drops below 7.0, the condition is called “acidosis” and frequently results in death. If it goes too high the results are similar. A pH meter can measure the value out to two decimal places reliably and consistently. The fact that any judge would suggest that 12.5 is includes in a 13 or greater simply illustrates that the judge has no clue what pH is about or its significance.

    1. 7.1

      Nice – but I am not certain that your context actually applies to the provided fact pattern.

      It may – I have not dived deeply into the actual facts, but the issue is not “precision required” — necessarily.

      If it does happen to BE a required precision, then the better path may well be one of lack of enablement if the patentee’s choice is too broad and cannot meet the claim in its breadth.

      Again, this is not because “ambiguous.” (to rebut comments from others)

    2. 7.2

      The issue here is not pH measurement accuracy. It is often more about filing patent applications as soon as possible, which means that critical parameters for effectiveness, which can be claimed, may not be that well defined at the date of filing for chemical and pharma patents.

      1. 7.2.1

        While the issue you suggest MAY be AN issue in this matter (and for the types of matters you suggest — given my own past views on how Pharma so often files before they actually possess the claimed utility as shown in the number of
        at the FDA), the point being discussed here IS in fact the rather simple notion of significant digits.

        Feel free to make other points.
        Do NOT dismiss the actual point at hand.

  6. 6

    Surprised the intrinsic extensive narrowing claim amendments in prosecution noted in the opinion did not decided the issue for them, but: “In short, the prosecution history shows that the Examiner drew a distinction between the stability of a composition with a pH of 13 and that of 12. Such distinction, however, does not illuminate the narrower issue of whether a pH of 13 could encompass values that round to 13, in particular 12.5. .. We find that this case is one where the proper claim construction cannot be reached without the aid of extrinsic evidence, and that the district court should have considered, at minimum, the textbook excerpts offered and addressed by the parties.”

  7. 5

    “Requiring patent applicants to explicitly identify the precision and error margin for measurements during prosecution would prevent the need for courts to resort to extrinsic evidence to resolve ambiguity that should have been addressed before issuance. This would increase certainty around claim scope and reduce unnecessary litigation.”

    Yes, that. Inexcusable that in this day and age such numerical disputes exist at all.

    Having to leave the disclosure to root around like pigs looking for truffles in extrinsic evidence is ridiculous.

    Say what you mean; mean what you say.

    Faced with numerical variables and uncertainties?

    WRITE MORE CLAIMS to address such.


  8. 4

    No matter what you do, the Examiner is going to try to jam the round peg into the square hole….every time.

  9. 3

    Of course the PTO should be more diligent about holding applicants feet to the fire on issues like this. But beyond that, the rule should be that these farcical “disputes” over the literal scope of plain language (“does greater than 13 include less than 13”) should ALWAYS be resolved against the patentee. That’s because the patentee has the sole ability to ensure that there is claim language that covers the alleged invention and excludes the prior art. The patentee chooses the words and then — drum roll, please — has to live with them.

    1. 3.1

      I think that in your hurry to blame the applicant (shockers), you have forgotten that the actual issue here is Examination ‘Quality.’

      While certainly applicants can ‘choose p00rly,’ those doing so should be even easier to examine properly.

    2. 3.2

      The claims need to allow for some flexibility for standard errors in measurement. In the case in which the error in measurement would read on the prior art, the patentee will have to be more precise in the claim, or risk a finding of invalidity.

      1. 3.2.1

        Close PM – standard errors is definitely a consideration (as would the legal fiction of Person Having Ordinary Skill In The Art immediately recognize).

  10. 2

    This would unfairly force inventors to define their inventions before identifying possible infringers.

    1. 2.1

      The Framers would be appalled to learn of the current restrictions placed on patent seekers, particularly the forced reliance on the use of words to describe things and the hiring of non-elected citizens to examine the applications. Patents should be self-granting and enforced in the same way that the Framers intended every Constitutionally authorized law in the land to be enforced: at the point of a powerful semi-automatic rifle.

  11. 1

    I’ve had cases with a difference of 0.1 pH between the prior art and claims. A lot of times attorneys will point out that pH is a log scale. So a pH of 13 is is 10 times more acidic than a pH of 12.

    1. 1.2

      (Where’s the headsmacking emoji when I need it?)

      Not only this, but it’s important to remember that pH can only precisely, let alone accurately, be measured once a solution has reached equilibrium — and with some salts (the specification and illustrative claim quoted in the opinion for this patent is for a salt) and many biological compounds this can take hours and even longer. And for this patent, that’s particularly ironic because the stated purpose of the invention was for a formulation that would be stable over an extended period without refrigeration. Thus, one might infringe 30 seconds after adding the critical compound to water but not three days later — or vice versa, depending upon the actual compounds and sometimes other conditions.

      So even just specifying a more-digits-stated range (and “greater than” is also a range) would be insufficient. The standard for an acceptable application should require all of the information that would be necessary to grade a junior/senior-level lab writeup… and if that requires getting away from the “every claim is a single sentence” nonsense, all the better.

      1. 1.2.1

        Riffing on this, if you’re “invention” is all about some measurable improvement in stability that flows from a change in one or two components (like hydrogen ion concentration) then for goodness sake the details for measuring that changed component need to be provided and there should be side-by-side comparison data with the closest known prior art showing the unexpected benefit. Can you get a patent without doing this? Sure, if you’re lucky. Should you be able to enforce that kind of weak patent to shut down a competitor or obtain millions of dollars in damages? Absolutely not.

      2. 1.2.2

        Jaws, I wonder if you have been reading the written decision of the EPO Board of Appeal of 2nd Feb 2021, revoking Patent 1993557 (patent family to US 8318802) for want of novelty. Your reasoning and theirs have much in common.

        That said, there is a very recent decision of the patent court in England construing a claim with text something like “not less than 13” to cover values somewhat less than 13. Every case turns on its own unique matrix of fact.

        Here, claim 1 of the EP as granted reads “A bulk solution containing (a)….(b) ….and (c)….wherein the bulk solution has a pH of 13 or higher.”


          I have now found the English case, Heraeus vs First Light. It’s physics rather than chemistry but that’s good because fact-finding is simpler.

          The CIPA case report in the current issue of its Journal includes the following paragraph:

          “The claims required a sealing glass bead not bigger than
          the diameter of the tube. First Light’s process used a
          bigger sealing glass bead. Heraus put its infringement
          case in three ways: that on a purposive construction
          the term ‘not bigger’ covered sealing glass beads
          bigger than the diameter of the tube within a tolerance;
          that in some cases the First Light sealing glass bead
          would inadvertently be smaller than the diameter of
          the tube, leading to literal infringement; and that there
          was infringement under the doctrine of equivalents”.

          The court found literal infringement of this claim.


          <sarcasm> I would have said “want of satisfactory laboratory technique,” but that’s not a legal ground for invalidation. Whether it should be is for another time. </sarcasm>

          In actual answer to the question: No. I was, instead, indirectly invoking the grading practices for when I was active in chemistry laboratories (back when we still had to bend and join our own glassware). That is, I didn’t care about the law — and, more particularly, about more-scientifically-aware-than-most-lawyers-but-still-not-lab-rats examiners — nearly as much as the inadequate communication to a POSITA for an art in which I’m aware of the communication standards of the relevant persons. Fundamental principle in a chemistry lab: Your results are meaningless without specifically stating the context of your test. Water only boils at 100C when ambient (that is, at equilibrium!) pressure is 101.325Pa; and this affects the boiling point of everything else, too.


            Very true, Jaws – but as you may be aware (you may not be), patents are legal documents rather than engineering documents.

            There is a rather large leeway given certain legal fictions (e.g., PHOSITA).


              I’m all too aware. I’m a second-career lawyer who (unlike over 90% of the district court judges who are confronted with patent matters) has a laboratory STEM degree. Being second-career means it’s not just allowed, but almost mandatory, to criticize legalism foolishness that is orthogonal to reality, especially when it’s condescendingly superior to the very subjects of disputes brought before it. See, e.g., Myriad (Scalia, J., concurring).

              Patent specifications, examinations, and issuance is just one example.


                I don’t recognize what you think you mean by “legalism f00lishness,” but you certainly have let your ego and a past life “laboratory STEM degree” overtake your emotions in your response (my point about patents not being engineering documents is a entirely accurate) — check your own condescension — it’s out of place.

                (If you are going to put that ego in a boat, your going to need a bigger boat)

                1. Really? I criticize a particular context in which legal egos allow them to dismiss the doctrine, language, and expectations of the other subject fields (the narrow one here being one in which I have both subject-field and legal expertise) in which those with only legal training are “resolving disputes,” and that’s my ego that’s a problem? Now I really need that head-smack emoji.

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