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Nature of Suit Code: 830
Nature of Suit: Patent
Cause of Action: 

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United States Court of Appeals 

for the Federal Circuit ______________________ 

BIOSIG INSTRUMENTS, INC.,

Plaintiff-Appellant

v.

NAUTILUS, INC.,

Defendant-Appellee

______________________ 

2012-1289

______________________ 

Appeal from the United States District Court for the 

Southern District of New York in No. 10-CV-7722, Judge 

Alvin K. Hellerstein.

______________________ 

Decided: April 27, 2015 

______________________ 

MARK DAVID HARRIS, Proskauer Rose LLP, New York, 

NY, argued for plaintiff-appellant. Also represented by 

PAUL MILCETIC, Villanova, PA; TODD KUPSTAS, Kessler 

Topaz Meltzer & Check, LLP, Radnor, PA; DANIEL C.

MULVENY, Barnes & Thornburg LLP, Wilmington, DE; 

JOHN E. ROBERTS, Proskauer Rose LLP, Boston, MA.

JOHN D. VANDENBERG, Klarquist Sparkman, LLP, 

Portland, OR, argued for defendant-appellee. Also 

represented by JAMES E. GERINGER, PHILIP J. WARRICK,

JEFFREY S. LOVE. 

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______________________ 

Before NEWMAN, SCHALL, and WALLACH, Circuit Judges.

WALLACH, Circuit Judge.

This case is before us on remand from the United 

States Supreme Court. Biosig Instruments, Inc. (“Biosig”) 

is the assignee of U.S. Patent No. 5,337,753 (“the ’753 

patent”), directed to a heart rate monitor associated with 

an exercise apparatus and/or exercise procedures. Biosig 

brought a patent infringement action against Nautilus, 

Inc. (“Nautilus”) in district court alleging that Nautilus 

infringed claims 1 and 11 of the ’753 patent. After claim 

construction, Nautilus filed a motion for summary 

judgment seeking, in relevant portion, to have the ’753 

patent held invalid for indefiniteness. The district court 

granted Nautilus’s motion, and Biosig appealed. This 

court found the claims at issue were not invalid for 

indefiniteness, and reversed and remanded for further 

proceedings. Nautilus petitioned for certiorari, and the 

Supreme Court vacated and remanded this court’s 

decision. On remand, we maintain our reversal of the 

district court’s determination that Biosig’s patent claims 

are indefinite. 

BACKGROUND

The facts of this case were recited in detail in this 

court’s previous opinion and need not be repeated in full 

here. Nautilus, Inc. v. Biosig Instruments, Inc. (Nautilus 

I), 715 F.3d 891, 898 (Fed. Cir. 2013) In summary, the 

’753 patent is directed to a heart rate monitor that 

purports to improve upon the prior art by effectively 

eliminating “noise” signals during the process of detecting 

a user’s heart rate. ’753 patent col. 1 ll. 5–10. The ’753 

patent discloses an apparatus preferably mounted on 

exercise equipment that measures heart rates by, inter 

alia, processing electrocardiograph (“ECG”) signals from 

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which electromyogram (“EMG”) signals are substantially 

removed. Id. col. 1. ll. 36–41. Claim 1 is representative 

and recites, in relevant part:

1. A heart rate monitor for use by a user in 

association with exercise apparatus and/or 

exercise procedures, comprising:

an elongate member;

electronic circuitry including a difference 

amplifier having a first input terminal of a first 

polarity and a second input terminal of a second 

polarity opposite to said first polarity;

said elongate member comprising a first half and 

a second half;

a first live electrode and a first common electrode 

mounted on said first half in spaced relationship

with each other;

a second live electrode and a second common 

electrode mounted on said second half in spaced 

relationship with each other;

said first and second common electrodes being 

connected to each other and to a point of common 

potential . . . .

Id. col. 5 ll. 17–36 (emphases added). 

Biosig sued Nautilus for infringement of the ’753 

patent in August 2004. After several reexamination 

proceedings, Biosig reinstituted a patent infringement 

action against Nautilus on October 8, 2010. On August 

11, 2011, the district court conducted a Markman hearing, 

and on September 29, 2011, issued its order construing 

certain disputed claim terms. On November 10, 2011, 

Nautilus moved under Federal Rule of Civil Procedure 56 

for summary judgment on two issues: infringement and 

invalidity for indefiniteness. On February 22, 2012, the 

district court granted Nautilus’s motion, holding the ’753 

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patent’s “spaced relationship” term as recited in claim 1 

was indefinite as a matter of law. The court did not 

decide the issue of infringement. 

On appeal, this court reversed and remanded. Citing 

precedent, we stated that a claim is indefinite “only when 

it is ‘not amenable to construction’ or ‘insolubly 

ambiguous.’” Nautilus I, 715 F.3d at 898 (quoting 

Datamize, LLC v. Plumtree Software, Inc., 417 F.3d 1342, 

1347 (Fed. Cir. 2005)). Under that standard, we

determined the ’753 patent survived indefiniteness 

review. Considering the “intrinsic evidence,” we found 

that it provided “certain inherent parameters of the 

claimed apparatus, which to a skilled artisan may be 

sufficient to understand the metes and bounds of ‘spaced 

relationship.’” Id. at 899. 

The Supreme Court granted certiorari, 134 S. Ct. 896 

(2014), and, rejecting our “not amenable to construction or 

insolubly ambiguous” standard, vacated and remanded. 

Nautilus, Inc. v. Biosig Instruments, Inc. (Nautilus II), 

134 S. Ct. 2120 (2014). In its decision, the Court 

articulated the standard to be applied: “[W]e hold that a 

patent is invalid for indefiniteness if its claims, read in 

light of the specification delineating the patent, and the 

prosecution history, fail to inform, with reasonable 

certainty those skilled in the art about the scope of the 

invention.” Id. at 2124 (emphasis added).

This court has jurisdiction pursuant to 28 U.S.C. 

§ 1295(a)(1) (2012).

DISCUSSION 

I. Standard of Review & Legal Framework

A patent must “conclude with one or more claims 

particularly pointing out and distinctly claiming the 

subject matter which the applicant regards as [the] 

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invention.” 35 U.S.C. § 112 ¶ 2 (2006).1 A claim is invalid 

for indefiniteness if its language, when read in light of the 

specification and the prosecution history, “fail[s] to 

inform, with reasonable certainty, those skilled in the art 

about the scope of the invention.” Nautilus II, 134 S. Ct. 

at 2124. We review the district court’s indefiniteness 

determination de novo. Interval Licensing LLC v. AOL, 

Inc., 766 F.3d 1364, 1370 (Fed. Cir. 2014). 

A patent is presumed valid under 35 U.S.C. § 282 and, 

“consistent with that principle, a [fact finder is] instructed 

to evaluate . . . whether an invalidity defense has been 

proved by clear and convincing evidence.” Microsoft Corp. 

v. i4i Ltd. P’ship, 131 S. Ct. 2238, 2241 (2011). 

“In the face of an allegation of indefiniteness, general 

principles of claim construction apply.” Enzo Biochem, 

Inc. v. Applera Corp., 599 F.3d 1325, 1332 (Fed. Cir. 2010) 

(internal quotation marks and citation omitted). “In that 

regard, claim construction involves consideration of 

primarily the intrinsic evidence, viz., the claim language, 

the specification, and the prosecution history.” Id. 

Though the ultimate construction of a claim term is a 

legal question reviewed de novo, underlying factual 

determinations made by the district court based on 

extrinsic evidence are reviewed for clear error. Teva 

Pharm. USA, Inc. v. Sandoz, Inc., 135 S. Ct. 831, 842 

(2015). In contrast, “when the district court reviews only 

evidence intrinsic to the patent (the patent claims and 

specifications, along with the patent’s prosecution 

history), the judge’s determination will amount solely to a 

1 Paragraph 2 of 35 U.S.C. § 112 was replaced with 

newly designated § 112(b) when § 4(c) of the Leahy–Smith 

America Invents Act (“AIA”), Pub. L. No. 112–29, took 

effect on September 16, 2012. Because the application 

resulting in the patent was filed before that date, we will 

refer to the pre-AIA version of § 112.

 

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determination of law, and the Court of Appeals will 

review that construction de novo.” Id. at 841. 

When a “word of degree” is used, the court must 

determine whether the patent provides “some standard 

for measuring that degree.” Enzo Biochem, 599 F.3d at 

1332; Seattle Box Co., Inc. v. Indus. Crating & Packing, 

Inc., 731 F.2d 818, 826 (Fed. Cir. 1984). Recently, this 

court explained: “[w]e do not understand the Supreme 

Court to have implied in [Nautilus II], and we do not hold 

today, that terms of degree are inherently indefinite. 

Claim language employing terms of degree has long been 

found definite where it provided enough certainty to one 

of skill in the art when read in the context of the 

invention.” Interval Licensing, 766 F.3d at 1370. 

Moreover, when a claim limitation is defined in “purely 

functional terms,” a determination of whether the 

limitation is sufficiently definite is “highly dependent on 

context (e.g., the disclosure in the specification and the 

knowledge of a person of ordinary skill in the relevant art

area).” Halliburton Energy Servs., Inc. v. M-I LLC, 514 

F.3d 1244, 1255 (Fed. Cir. 2008).

Prior to the Supreme Court’s decision in this case, a 

claim was indefinite when it was “insolubly ambiguous” or 

“not amenable to construction.” Datamize, 417 F.3d at 

1347 (internal quotations and citations omitted). In 

Nautilus II, the Supreme Court observed that § 112, ¶ 2 

requires “a delicate balance.” 134 S. Ct. at 2128 (quoting 

Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 

U.S. 722, 731 (2002)). On one hand, the Court noted, the 

definiteness requirement must take into account the 

inherent limitations of language. “Some modicum of 

uncertainty,” the Court recognized, is the “‘price of 

ensuring the appropriate incentives for innovation.’” Id.

(quoting Festo Corp, 535 U.S. at 741). On the other hand, 

the Court explained, a patent must be precise enough to 

afford clear notice of what is claimed, thereby “appris[ing] 

the public of what is still open to them. Otherwise there 

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would be a zone of uncertainty which enterprise and 

experimentation may enter only at the risk of 

infringement claims.” Id. at 2129 (internal quotation 

marks and citations omitted). The Court further

explained the policy rationale: “absent a meaningful 

definiteness check . . . patent applicants face powerful 

incentives to inject ambiguity into their claims.” Id. 

Balancing these competing interests, the Supreme 

Court held that “[t]o determine the proper office of the 

definiteness command, . . . we read § 112, ¶ 2 to require 

that a patent’s claims, viewed in light of the specification 

and prosecution history, inform those skilled in the art 

about the scope of the invention with reasonable 

certainty.” Id. (emphasis added). “The standard adopted” 

by the Supreme Court “mandates clarity, while 

recognizing that absolute precision is unattainable.” Id.

at 2129. It also accords with opinions of the Court stating 

that “the certainty which the law requires in patents is 

not greater than is reasonable, having regard to their 

subject-matter.” Id. (quoting Minerals Separation, Ltd. v. 

Hyde, 242 U.S. 261, 270 (1916) (emphasis added)). 

II. The Sole Issue Presented Here Is Indefiniteness

On remand from the Supreme Court, the sole issue 

presented to this court is whether the district court erred 

in holding the ’753 patent invalid for indefiniteness. In 

particular, the district court held that “spaced 

relationship” as recited in claim 1, and referring to the 

spacing between the common and live electrodes, was not 

distinctly pointed out and particularly claimed in the 

patent in violation of 35 U.S.C. § 112, ¶ 2.

Before this court, Nautilus and Biosig dispute 

whether the Supreme Court articulated a new, stricter 

standard or whether, in rejecting the phrases “insolubly 

ambiguous” and “amenable to construction,” the Court 

was primarily clarifying that a patent’s claims must 

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inform those skilled in the art with “reasonable certainty” 

of what is claimed.

Nautilus argues the Supreme Court’s mandate 

requires this court to find the term “spaced relationship” 

indefinite because “the original intrinsic evidence point[s] 

in two opposite directions, leaving the claims’ 

boundaries—and thus the potential avenues for follow-on 

innovation—fundamentally uncertain.” Nautilus’s Supp. 

Br. 14. According to Nautilus, “spaced relationship” could 

mean “a special spacing critical in some way to the recited 

result” or it could mean the opposite, that it is not limited 

or linked by the recited result. Id. at 14, 17.

Biosig counters that “‘reasonable certainty’ is not a 

new standard; it is the degree of clarity in patent claiming 

that has governed for nearly one hundred years.” Biosig’s 

Supp. Br. 3. According to Biosig, “the Supreme Court did 

not indicate that [this court, in Nautilus I,] had been led 

astray by either of the disapproved phrases. Its main 

concern, rather, was that the use of those phrases by the 

Federal Circuit could send the wrong message to district 

courts and the patent bar.” Id. at 4 (citing Nautilus II, 

134 S. Ct. at 2130 & n.8).

III. Reasonable Certainty Under Nautilus II Is a 

Familiar Standard

As the Supreme Court emphasized in Nautilus II, 

§ 112 “requires that a patent specification ‘conclude with 

one or more claims particularly pointing out and 

distinctly claiming the subject matter’” of the invention. 

134 S. Ct. at 2124. The Court found too imprecise our 

“insolubly ambiguous” standard, and instead held that “a 

patent is invalid for indefiniteness if its claims, read in 

light of the specification delineating the patent, and the 

prosecution history, fail to inform, with reasonable 

certainty, those skilled in the art about the scope of the 

invention.” Id. (emphasis added). 

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The Court has accordingly modified the standard by 

which lower courts examine allegedly ambiguous claims; 

we may now steer by the bright star of “reasonable 

certainty,” rather than the unreliable compass of 

“insoluble ambiguity.” 

Reasonableness is the core of much of the common 

law, and “reasonable certainty” has been defined in broad 

spectra of the law. See, e.g., Palsgraf v. Long Island R.R. 

Co., 162 N.E. 99 (N.Y. 1928) (explaining the “reasonable 

[person]” foreseeability standard in tort); cf. Jay v. Sec’y of 

Dep’t of Health & Human Servs., 998 F.2d 979, 984 (Fed. 

Cir. 1993) (discussing whether a reasonable person could 

conclude a certain vaccine caused the child’s death). The 

Supreme Court has articulated a spectrum for 

interpretation of the phrase “reasonable certainty.”2 

 2 Prior to Nautilus II, the Court discussed 

“reasonable certainty” on numerous occasions. See, e.g., 

Kelo v. City of New London, 545 U.S. 469, 487–88 (2005) 

(where petitioners argued the Court should require 

“reasonable certainty” that expected public benefits in a 

takings case would actually accrue, the Court declined to 

impose that “heightened form of review”); Allentown Mack 

Sales & Serv., Inc. v. Nat’l Labor Review Bd., 522 U.S. 

359, 369 (1998) (express disavowals by more than half of 

an employee bargaining unit would establish reasonable 

certainty of union nonsupport); Coffy v. Republic Steel 

Corp., 447 U.S. 191, 197–99 (1980) (explaining “there 

must be a reasonable certainty that the benefit would 

have accrued if the employee had not gone into the 

military service”); Ala. Power Co. v. Davis, 431 U.S. 581, 

587–88, 591 (1977) (reasonable certainty requirement for 

accrual of benefits in veteran’s reemployment case 

satisfied where work history demonstrates veteran “would 

almost certainly have accumulated accredited service”); 

Tilton v. Mo. Pac. R.R. Co., 376 U.S. 169, 180–81 (1964); 

Boyce Motor Lines v. United States, 342 U.S. 337, 340 

 

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(1952) (notice of conduct required by criminal statute 

must be sufficiently definite to guide its application, 

however “[t]he requirement of reasonable certainty does 

not preclude the use of ordinary terms to express ideas 

which find adequate interpretation in common usage and 

understanding”) (emphasis added) (citation omitted);

United States v. Penn. Foundry & Mfg. Co., 337 U.S. 198, 

207–08 (1949) (declining to accept the Court of Claims 

“rough estimate” as providing the reasonable certainty 

required for establishing damages); United Carbon Co. v. 

Binney & Smith Co., 317 U.S. 228, 234 (1942) (“What on 

first impression [in a patent infringement action] appears 

to be reasonable certainty of dimension disappears when 

we learn that ‘approximately one-sixteenth of an inch in 

diameter’ includes a variation from approximately 1/4th 

to 1/100th of an inch. So read, the claims are but 

inaccurate suggestions of the functions of the product.”) 

(emphasis added); Palmer v. Conn. Ry. & Lighting Co., 

311 U.S. 544, 558, 561 (1941) (“Certainty in the fact of 

damage is essential. [Reasonable] [c]ertainty as to the 

amount goes no further than to require a basis for a 

reasoned conclusion.”); Sheldon v. Metro-Goldwyn 

Pictures Corp., 309 U.S. 390, 404 (1940) (analogizing 

copyright damages to patent infringement, the Court 

found a reasonable certainty requirement satisfied not 

with “mathematical exactness,” but only a “reasonable 

approximation”); Sproles v. Binford, 286 U.S. 374, 393 

(1932) (“The requirement of reasonable certainty does not 

preclude the use of ordinary terms to express ideas which 

find adequate interpretation in common usage and 

understanding,”); Hamilton-Brown Shoe Co. v. Wolf Bros. 

& Co., 240 U.S. 251, 261–62 (1916) (analogizing 

trademark damages to patent damages and holding “[t]he 

difficulty lies in ascertaining what proportion of the profit 

is due to the trademark . . . and as this cannot be 

ascertained with any reasonable certainty, it is more 

consonant with reason and justice that the owner of the 

 

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Following the issuance of Nautilus II, this court 

applied the reasonable certainty standard in DDR 

Holdings, LLC v. Hotels.com, 773 F.3d 1245, 1260–61 

(Fed. Cir. 2014). (after analogizing to facts from prior 

cases and applying a “reasonable certainty” standard, 

finding the term “look and feel” had an established 

meaning in the art as demonstrated by the trial record, 

thus informing those skilled in the art with reasonable 

certainty). In Interval Licensing, the “reasonable 

certainty” test was applied to determine whether one of 

the embodiments provided “a reasonably clear and 

exclusive definition,” with a focus on the “relationship” 

between the embodiments and the claim language, and 

whether the embodiments created “objective boundaries”

for those skilled in the art. 766 F.3d at 1371. The court 

also stated: 

trademark should have the whole profit than that he 

should be deprived of any part of it by the fraudulent act 

of the defendant”); Ont. Land Co. v. Yordy, 212 U.S. 152, 

157 (1909) (“The first requisite of an adequate description 

is that the land shall be identified with reasonable 

certainty; but the degree of certainty required is always 

qualified by the application of the rule that that is certain 

which can be made certain.”) (quoting Jones on Law of 

Real Property in Conveyancing § 323); Hetzel v. Balt. & 

Ohio R.R. Co., 169 U.S. 26, 38 (1898) (“In many cases 

[proof which excludes the possibility of a doubt] cannot be 

given, and yet there might be a reasonable certainty, 

founded upon inferences legitimately and properly 

deducible from the evidence . . . .”); United States v. 

Smith, 18 U.S 153, 160–62 (1820) (the crime of piracy is 

defined by the law of nations with reasonable certainty); 

cf. Bell Atl. Corp. v. Twombly, 550 U.S. 544, 578 n.5 

(2007) (Stevens, J., dissenting); Boyde v. California, 494 

U.S. 370, 393 n.2 (1990); Thor Power Tool Co. v. Comm’r, 

439 U.S. 522, 543–44 (1979); Pub. Util. Comm’n v. United 

States, 355 U.S. 534, 552 (1958). 

 

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We do not understand the Supreme Court to have 

implied in Nautilus [II], and we do not hold today, 

that terms of degree are inherently indefinite. . . . 

Although absolute or mathematical precision is 

not required, it is not enough as some of the 

language in our prior cases may have suggested to 

identify “some standard for measuring the scope 

of the phrase.” . . . The patents’ “unobtrusive 

manner” phrase is highly subjective, and, on its 

face, provides little guidance to one of skill in the 

art. . . . The patents contemplate a variety of 

stimuli that could impact different users in 

different ways. As we have explained, a term of 

degree fails to provide sufficient notice of its scope 

if it depends on the unpredictable vagaries of any 

one person’s opinion.

Id. at 1371–72 (citations omitted); see also Augme Techs. 

v. Yahoo!, Inc., 755 F.3d 1326, 1340 (Fed. Cir. 2014) (A 

limitation “clear on its face” “unquestionably meets [the 

Nautilus II] standard.”). 

In the wake of Nautilus II, judges have had no 

problem operating under the reasonable certainty 

standard. For example, Judge Bryson, sitting by 

designation in Texas, stated: “Indefiniteness is a legal 

determination; if the court concludes that a person of 

ordinary skill in the art, with the aid of the specification, 

would understand what is claimed, the claim is not 

indefinite.” Freeny v. Apple Inc., No. 2:13-CV-00361-

WCB, 2014 WL 4294505, at *4 (E.D. Tex. Aug. 28, 2014)

(describing the question as whether “a person of ordinary 

skill can discern from the claims and specification what 

the bounds of the claim are with reasonable certainty”). 

After listing numerous fact-specific examples, Judge 

Bryson noted that “[c]ontrary to the defendant’s 

suggestion, [the Nautilus II] standard does not render all 

of the prior Federal Circuit and district court cases 

inapplicable” and “all that is required is that the patent 

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apprise [ordinary-skilled artisans] of the scope of the 

invention.” Id. at *5.3 

3 Prior to Nautilus II, a number of our cases 

applied a reasonable certainty standard in various 

contexts. See, e.g., ICU Med., Inc. v. Alaris Med. Sys., 558 

F.3d 1368, 1375 (Fed. Cir. 2009) (discussing the

importation of limitations from the specification into the 

claims, noting that “the line between construing terms 

and importing limitations can be discerned with

reasonable certainty and predictability if the court’s focus 

remains on how a person of ordinary skill in the art would 

understand the claim terms”) (quoting Phillips v. AWH 

Corp., 415 F.3d 1303, 1323 (Fed. Cir. 2005) (en banc)). In 

a lost profits damages analysis, we noted the amount 

“need not be proved with unerring precision” and held 

that lost profits had been proved with reasonable 

certainty and that a district court finding to the contrary 

was clearly erroneous where the dealer profit margin was 

“roughly twenty-five percent of the dealer price.” Ryco, 

Inc. v. Ag-Bag Corp., 857 F.2d 1418, 1428 (Fed. Cir. 1988) 

(citations omitted). In In re Clarke, 356 F.2d 987, 992 

(CCPA 1966), our predecessor court held that “where it 

can be concluded that facts . . . in support of a general 

allegation of conception and reduction to practice . . . 

would persuade one of ordinary skill in the art to a 

reasonable certainty that the applicant possessed so much 

of the invention as to encompass the reference disclosure,

then that showing should be accepted as establishing a 

prima facie case of inventorship.” Finally, our 

predecessor noted, in Young v. Bullitt, 233 F.2d 347, 351 

(CCPA 1956), that in a priority contest in a patent 

interference, “[t]he question generally is whether, when 

all the circumstances are considered together, there is a 

reasonable certainty as to the identity of the product. 

Proof beyond a reasonable doubt is not necessary where 

applications were copending.”

 

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IV. Biosig’s Claims Inform a Skilled Artisan With 

Reasonable Certainty 

Considering this background, and the Supreme 

Court’s articulated concerns in Nautilus II (the 

necessarily inexact balance between “the inherent 

limitations of language” and the “modicum of uncertainty” 

which is “the price of ensuring the appropriate incentives 

for innovation,” on the one hand, and, on the other, 

enough precision “to afford clear notice of what is 

claimed”), we conclude that Biosig’s claims inform those 

skilled in the art with reasonable certainty about the 

scope of the invention. Nautilus II, 134 S. Ct. at 2128–29

(internal quotation marks and citations omitted). As we 

have stated in the past, “[t]he degree of precision 

necessary for adequate claims is a function of the nature 

of the subject matter.” Miles Labs., Inc. v. Shandon, Inc., 

997 F.2d 870, 875 (Fed. Cir. 1993) (citing Hybritech Inc. v. 

Monoclonal Antibodies, Inc., 802 F.2d 1367, 1375 (Fed. 

Cir. 1986)). 

On certiorari, the Supreme Court “express[ed] no 

opinion on the validity of the patent-in-suit” but rather 

instructed this court “to decide the case employing the 

standard we have prescribed.” Nautilus II, 134 S. Ct. at 

2124.

As an initial matter, since our decision in Nautilus I, 

the Supreme Court determined in Teva Pharmaceuticals 

USA v. Sandoz that “when the district court reviews only 

evidence intrinsic to the patent (the patent claims and 

specifications, along with the patent’s prosecution 

history), the judge’s determination will amount solely to a 

determination of law, and the Court of Appeals will 

review that construction de novo.” 135 S. Ct. at 841. 

However, “when the district court looks beyond the 

intrinsic evidence and consults extrinsic evidence, for 

example to understand the relevant science, these 

subsidiary fact findings are reviewed for clear error.” 

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Enzo Biochem Inc. v. Applera Corp., No. 2014-1321, 2015 

WL 1136421, at *4 (Fed. Cir. Mar. 16, 2015). 

Our prior analysis primarily relied on intrinsic 

evidence and we found the “extrinsic evidence 

underscores the intrinsic evidence.” Nautilus I, 715 F.3d 

at 901. We revisit the intrinsic evidence here to make 

clear that a skilled artisan would understand with 

reasonable certainty the scope of the invention. 

In relevant part, we noted an ordinarily skilled 

artisan would be able to determine this language requires 

the spaced relationship to be neither infinitesimally small 

nor greater than the width of a user’s hands. Specifically, 

we stated:

[T]he district court is correct that the specification 

of the ’753 patent does not specifically define 

“spaced relationship” with actual parameters, e.g., 

that the space between the live and common 

electrodes is one inch. Nevertheless, the ’753 

patent’s claim language, specification, and the 

figures illustrating the “spaced relationship” 

between the live and common electrodes are 

telling and provide sufficient clarity to skilled 

artisans as to the bounds of this disputed term. 

For example, on the one hand, the distance 

between the live electrode and the common 

electrode cannot be greater than the width of a 

user’s hands because claim 1 requires the live and 

common electrodes to independently detect 

electrical signals at two distinct points of a hand. 

On the other hand, it is not feasible that the 

distance between the live and common electrodes 

be infinitesimally small, effectively merging the 

live and common electrodes into a single electrode 

with one detection point. See ’753 patent col. 3 ll. 

26–31 (describing how each hand is placed over 

the live and common electrodes so that they are 

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“in physical and electrical contact with both 

electrodes”). 

Nautilus I, 715 F.3d at 899.

The prosecution history further illustrates that the 

term is not indefinite. In Nautilus I, we considered the 

functionality of the claimed heart rate monitor as recited 

in claim 1, “which provided the basis for overcoming the 

PTO’s office action rejections during the reexamination.” 

Id. Specifically, claim 1 provides, in part:

whereby, a first electromyogram signal will be 

detected between said first live electrode and said 

first common electrode, and a second 

electromyogram signal, of substantially equal 

magnitude and phase to said first electromyogram 

signal will be detected between said second live 

electrode and said second common electrode; so 

that, when said first electromyogram signal is 

applied to said first terminal and said second 

electromyogram signal is applied to said second 

terminal, the first and second electromyogram 

signals will be subtracted from each other to 

produce a substantially zero electromyogram 

signal at the output of said difference amplifier.

Id. col. 5 ll. 48–61. This “whereby” clause describes the 

function of substantially removing EMG signals that 

necessarily follows from the previously-recited structure 

consisting of the elongate member, the live electrode, and 

the common electrode. Id. col. 5 ll. 42–47. As we 

described in Nautilus I, 

[t]he EMG signal is detected between the live and 

common electrodes, which are in a “spaced 

relationship” with each other. Even more 

significantly, the PTO examiner found this 

function to be “crucial” as a reason for overcoming 

the cited prior art and confirming the 

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patentability of the asserted claims upon 

reexamination. J.A. 139–46. Thus, the recitation 

of this function in claim 1 is highly relevant to 

ascertaining the proper bounds of the “spaced 

relationship” between the live and common 

electrodes. See Hoffer v. Microsoft Corp., 405 F.3d 

1326, 1329 (Fed. Cir. 2005) (per curiam) (“[W]hen 

the ‘whereby’ clause states a condition that is 

material to patentability, it cannot be ignored in 

order to change the substance of the invention.”). 

Nautilus I, 715 F.3d at 900. Not only is the recitation of 

this function in claim 1 “highly relevant” to ascertaining 

the boundaries of the “spaced relationship” between the 

live and common electrodes, it shows 

a skilled artisan could apply a test and determine 

the “spaced relationship” as pertaining to the 

function of substantially removing EMG signals. 

Indeed, the test would have included a standard 

oscilloscope connected to both the inputs and 

outputs of the differential amplifier to view the 

signal wave forms and to measure signal 

characteristics. With this test, configurations 

could have been determined by analyzing the 

differential amplifier input and output signals for 

detecting EMG and ECG signals and observing 

the substantial removal of EMG signals from ECG 

signals while simulating an exercise. 

Id. at 900–1. 

As discussed in detail in Nautilus I, during 

prosecution, Biosig also presented evidence in the form of 

a declaration by the inventor, Mr. Gregory Lekhtman. 

See 01 Communique Lab., Inc. v. LogMeIn, Inc., 687 F.3d 

1292, 1298 (Fed. Cir. 2012) (considering statements made 

during reexamination as intrinsic evidence for purposes of 

claim construction). Mr. Lekhtman argued that when 

“configuring the claimed heart rate monitor, skilled 

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artisans can determine the ‘spaced relationship’ between 

live and common electrodes by calculating the point in 

which EMG signals are substantially removed.” Nautilus 

I, 715 F.3d at 900. As we explained, Mr. Lekhtman 

testified: 

[T]he strength of an EMG signal measurement is 

proportional to the space between the active and 

ground electrode and the size of the electrodes. 

J.A. 194–95. . . . [I]t was common knowledge for 

skilled artisans in 1992 that EMG potentials on 

each hand would be different, and that the ’753 

patent requires a configuration of the detectors 

that produce equal EMG signals from the left and 

right hands. J.A. 200. This equalization or 

balancing . . . is achieved by detecting EMG 

signals on the left and right palms, which are 

delivered to a differential amplifier in the EMG 

measuring device. Available design variables are 

then adjusted until the differential output is 

minimized, i.e., close to zero, and the ECG to 

EMG ratio is determined to be sufficient for an 

accurate heart rate determination. J.A. 200–01. 

Id. 

In this case, a skilled artisan would understand the 

inherent parameters of the invention as provided in the 

intrinsic evidence. The term “spaced relationship” does 

not run afoul of “the innovation-discouraging ‘zone of 

uncertainty’ against which [the Supreme Court] has 

warned,” and to the contrary, informs a skilled artisan 

with reasonable certainty of the scope of the claim. 

Interval Licensing, 766 F.3d at 1374 (quoting Nautilus II, 

134 S. Ct. at 2130). 

CONCLUSION

We conclude the “spaced relationship” phrase

“inform[s] those skilled in the art about the scope of the 

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invention with reasonable certainty.” The claims that 

include that phrase comply with Section 112 ¶2. 

REVERSED AND REMANDED

COSTS

Each party shall bear its own costs. 

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