  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 26, 2013
                ______________________

    MICHAEL J. BONELLA, Kessler Topaz Meltzer & Check
LLP, of Radnor, Pennsylvania, argued for plaintiff-
appellant. With him on the brief was PAUL B. MILCETIC.
Of counsel were TODD KUPSTAS and JENNA PELLECCHIA.

   JAMES E. GERINGER, Klarquist Sparkman, LLP, of
Portland, Oregon, argued for defendant-appellee. With
him on the brief were JOHN D. VANDENBERG and PHILIP
WARRICK.
                ______________________
2                  BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.


    Before NEWMAN, SCHALL, and WALLACH, Circuit Judges.
    Opinion for the court filed by Circuit Judge WALLACH.
     Concurring opinion filed by Circuit Judge SCHALL.
WALLACH, Circuit Judge.
    Biosig Instruments, Inc. (“Biosig”) is the assignee of
U.S. Patent No. 5,337,753 (“the ’753 patent”), which is
directed to a heart rate monitor associated with an exer-
cise apparatus and/or exercise procedures. Biosig brought
a patent infringement action against Nautilus, Inc.
(“Nautilus”) in district court alleging that Nautilus in-
fringed claims 1 and 11 of the ’753 patent. After claim
construction, Nautilus filed a motion for summary judg-
ment seeking, in relevant portion, to have the ’753 patent
held invalid for indefiniteness. The district court granted
Nautilus’s motion, and Biosig appealed. Because the
claims at issue are not invalid for indefiniteness, the
district court’s decision is reversed and remanded for
further proceedings.
                       BACKGROUND
                             I.
     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. According to
the patent, prior art monitors did not eliminate signals
given off by skeletal muscles (“electromyogram” or “EMG”
signals), which are brought about when users move their
arms or squeeze the monitor with their fingers. Id. col. 1
ll. 19–22. Because EMG signals are of the same frequen-
cy range as electrical signals generated by the heart
(“electrocardiograph” or “ECG” signals), EMG signals can
mask ECG signals rendering heart rate determination
while exercising difficult. Id. col. 1 ll. 22–25.
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.             3
    The ’753 patent discloses an apparatus preferably
mounted on exercise equipment that measures heart
rates by, inter alia, processing ECG signals from which
EMG signals are substantially removed. Id. col. 1. ll. 36–
41. The claimed heart rate monitor consists of an elon-
gate hollow cylindrical member that houses electronic
circuitry as illustrated below:




’753 patent fig. 1. A user’s left and right hands—100 and
200—each contact one of the “live” electrodes—9 and 13—
and one of the “common” electrodes—11 and 15—on either
end of the cylindrical member 3. Id. col. 2 ll. 50–64, col. 3
ll. 26–31. The electronic circuitry includes a difference
amplifier 23, which is connected to the live electrodes 9
and 13. Id. col. 3 ll. 7–10. The common electrodes 11 and
15 are connected to each other and to a point of common
potential, for example, a common ground. Id. col. 3 ll. 5–7.
An illustration of the circuitry is shown below:
4                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.




’753 patent fig. 2. Inputs 25 and 27 are of opposite polari-
ty. Id. col. 3 ll. 10–13. As the EMG signals and other
noise signals are of substantially equal amplitude and
phase, they cancel each other out in the difference ampli-
fier to provide a substantially zero output of EMG and
other noise signals. Id. col. 3 ll. 33–43. In contrast, ECG
signals, being of opposite phase, will be added and there-
fore further amplified in the difference amplifier so that
the output of the difference amplifier is substantially due
to the ECG signals only. Id. col. 3 ll. 44–50.
    Claim 1 is representative and recites, in relevant part:
    1. A heart rate monitor for use by a user in asso-
    ciation with exercise apparatus and/or exercise
    procedures, comprising:
    an elongate member;
    electronic circuitry including a difference amplifi-
    er 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;
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.            5
   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 elec-
   trode mounted on said second half in spaced rela-
   tionship with each other;
   said first and second common electrodes being
   connected to each other and to a point of common
   potential . . . .
’753 patent col. 5 ll. 17–36 (emphases added). In addition
to the capability of substantially removing EMG signals,
claim 1 recites a monitor, a means for measuring time
intervals between heart pulses, and a means for calculat-
ing the heart rate of a user using the measured time
intervals. See id. col. 5 l. 37–col. 6 l. 15.
     Asserted–dependent claim 11 further specifies that
the claimed “elongate member” is “mounted on an exer-
cise apparatus.” Id. col. 7 ll. 17–20. Figures 7 and 8 are
illustrative of a heart rate monitor mounted on a bicycle
and a stair-climbing exercise machine:
6                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.




Id. figs. 7–8.
                            II.
    The dispute between the parties has been ongoing for
years, stemming from the late 1990s when Biosig was in
discussions with Nautilus’s predecessor Stairmaster
Company regarding Biosig’s patented technology. Despite
these discussions, Stairmaster Company, and later Nauti-
lus, began selling exercise equipment that Biosig alleges
infringes its patented technology. These accused products
consist of heart rate monitors mounted on exercise
equipment.
     Biosig sued Nautilus for infringing the ’753 patent in
August 2004 (“2004 Action”). During the pendency of that
litigation, Nautilus twice sought ex parte reexamination of
the ’753 patent from the United States Patent and
Trademark Office (“PTO”).        The first reexamination
request was based primarily on U.S. Patent No. 4,444,200
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.              7
(“Fujisaki”).1 The PTO granted Nautilus’s request, and in
April 2009, the PTO issued an office action rejecting, inter
alia, claim 1 as anticipated by Fujisaki and claim 11 as
obvious over Fujisaki in view of other prior art references.
After Biosig filed its response to this PTO office action,
Nautilus requested a second reexamination of the ’753
patent, again, citing Fujisaki as the primary reference.
The PTO granted Nautilus’s second request for reexami-
nation, and the two reexamination proceedings were
consolidated in December 2009. The PTO ultimately
concluded these reexamination proceedings in June 2010
and confirmed the patentability of the ’753 patent without
amendment. During the pendency of this reexamination
proceeding, the parties voluntarily dismissed without
prejudice the claims and counterclaims of the 2004 Ac-
tion.
    Upon conclusion of the reexamination proceeding, Bi-
osig re-instituted 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




    1   Fujisaki relates to a system for measuring heart
pulse rate, and more particularly, to “a heart pulse rate
measuring system having a pair of grip sensors adapted
to be gripped with both hands for sensing heart pulse
signals.” Fujisaki, col. 1 ll. 5–9. “Each of the grip sensors
is composed of two conductive cylindrical electrodes
arranged in an axially aligned relationship and electrical-
ly insulated from each other.” Id. col 1 ll. 45–48. “The
electric circuit includes a differential amplifier having
inputs from the grip sensors for amplifying the difference
between the heart pulse signals . . . .” Id. col. 1 ll. 48–51.
8                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
disputed claim terms.2 On November 10, 2011, Nautilus
moved under Federal Rule of Civil Procedure 56 seeking
summary judgment on two issues: infringement and
invalidity for indefiniteness.
    On February 22, 2012, the district court held a hear-
ing on Nautilus’s motion for summary judgment. As to
the issue of infringement, the district court denied Nauti-
lus’s motion as premature because the parties had yet to
undertake significant discovery. Summ. J. Hr’g Tr. 5:23–
6:2, Biosig Instruments, Inc. v. Nautilus, Inc., No. 10–CV–
7722 (S.D.N.Y. Feb. 22, 2012), ECF No. 58 (“Summ. J.

    2   Even though the district court issued a claim con-
struction order, which included a construction of the
disputed term, “spaced relationship,” the record reflects
the district court nonetheless determined that “space
relationship” was ambiguous, and therefore, found Bi-
osig’s contentions pertaining to this term unpersuasive.
J.A. 1391:15–21 (August 11, 2011 Markman Hearing)
(“And we are going on to say, the spaced relationship
arises from trial and error placements of the two elec-
trodes on the cylindrical bar. Once placed they’re in a
space relationship. That spaced relationship must be
greater than the width of each electrode. What I’ve done
will confuse the jury and it may set up Mr. Milcetic for a
ruling of invalidity. Fair warning.”) (emphasis added);
J.A. 2819:16–2820:1 (February 22, 2012 Summary Judg-
ment Hearing) (“THE COURT: So he said a space[d]
relationship can be anything. It could be this or it could
be something else. MR. GERINGER: And, your Honor, at
the time, it was Mr. Bonella’s colleague, I believe, Mr.
Milcetic, but your Honor warned them that you didn’t
want them to fall into a trap. THE COURT: Right. MR.
GERINGER: That construing it in a way that embraces
ambiguity could lead to invalidity through vagueness.
THE COURT: And now you’re trying to take advantage of
that right now.”) (emphases added).
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.            9
Hr’g Tr.”). On invalidity, the district court granted Nauti-
lus’s motion, holding that the ’753 patent’s “spaced rela-
tionship” term as recited in claim 1 was indefinite as a
matter of law. Summ. J. Hr’g Tr. 51:21–52:1.
    After the parties completed summary judgment brief-
ing but before the hearing, Nautilus filed a third request
for reexamination of the ’753 patent on January 25, 2012,
and again, Nautilus cited Fujisaki as a primary prior art
reference. This time, on February 17, 2012, the PTO
denied Nautilus’s request, finding that there were no
substantial new questions of patentability raised by the
request. Biosig was notified of the PTO’s denial of Nauti-
lus’s third reexamination request after the district court’s
summary judgment hearing and decision. In light of this
new fact, Biosig moved for reconsideration of the district
court’s decision granting Nautilus’s motion for summary
judgment of invalidity, which the district court denied on
June 12, 2012. Biosig timely appeals. We have jurisdic-
tion pursuant to 28 U.S.C. § 1295(a)(1).
                       DISCUSSION
                               I.
    This court reviews the district court’s grant or denial
of motions for summary judgment under the law of the
regional circuit. MicroStrategy Inc. v. Bus. Objects, S.A.,
429 F.3d 1344, 1349 (Fed. Cir. 2005). The Second Circuit
reviews de novo a district court’s grant of a motion for
summary judgment. Kuebel v. Black & Decker Inc., 643
F.3d 352, 358 (2d Cir. 2011). Summary judgment motions
may be granted only where “there is no genuine dispute
as to any material fact and the movant is entitled to
judgment as a matter of law.” Fed. R. Civ. P. 56(a). In
making this determination, a court must “draw all rea-
sonable inferences in favor of the nonmoving party, and it
may not make credibility determinations or weigh the
evidence.” Reeves v. Sanderson Plumbing Prods., Inc., 530
U.S. 133, 150 (2000).
10                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
                             II.
    The sole issue presented to this court is whether the
district court erred in holding that the asserted claims of
the ’753 patent is invalid for indefiniteness as a matter of
law. 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 and particularly claimed in the patent in viola-
tion of 35 U.S.C. § 112, ¶ 2.3
    Indefiniteness is a legal issue this court reviews with-
out deference. Star Scientific, Inc. v. R.J. Reynolds Tobac-
co Co., 655 F.3d 1364, 1373 (Fed. Cir. 2011) (“Star
Scientific II”). Section 112, ¶ 2, requires that the specifi-
cation of a patent “conclude with one or more claims
particularly pointing out and distinctly claiming the
subject matter which the applicant regards as his inven-
tion.” “Because claims delineate the patentee’s right to
exclude, the patent statute requires that the scope of the
claims be sufficiently definite to inform the public of the
bounds of the protected invention, i.e., what subject
matter is covered by the exclusive rights of the patent.”
Halliburton Energy Servs., Inc. v. M-I LLC, 514 F.3d
1244, 1249 (Fed. Cir. 2008).
     A claim is indefinite only when it is “not amenable to
construction” or “insolubly ambiguous.” Datamize, LLC v.
Plumtree Software, Inc., 417 F.3d 1342, 1347 (Fed. Cir.
2005) (internal quotations and citations omitted). “In and
of itself, a reduction of the meaning of a claim term into
words is not dispositive of whether the term is definite . . .

     3   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. Nevertheless, the pre-AIA
version of § 112 applies because the ’753 patent issued
prior to that date.
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.           11
. And if reasonable efforts at claim construction result in
a definition that does not provide sufficient particularity
and clarity to inform skilled artisans of the bounds of the
claim, the claim is insolubly ambiguous and invalid for
indefiniteness.” Star Scientific, Inc. v. R.J. Reynolds
Tobacco Co., 537 F.3d 1357, 1371 (Fed. Cir. 2008) (“Star
Scientific I”) (citations omitted). “Thus, a construed claim
can be indefinite if the construction remains insolubly
ambiguous . . . .” Star Scientific II, 655 F.3d at 1373; see
also Exxon Research & Eng’g Co. v. United States, 265
F.3d 1371, 1377–79 (Fed. Cir. 2001) (accepting the district
court’s claim construction and separately undertaking an
analysis of the claims at issue to determine indefinite-
ness); Union Pac. Res. Co. v. Chesapeake Energy Corp.,
236 F.3d 684, 689–90, 692 (Fed. Cir. 2001) (same); Minn.
Min. and Mfg. Co. v. Johnson & Johnson Orthopaedics,
Inc., 976 F.2d 1559, 1567 (Fed. Cir. 1992) (same).
     General principles of claim construction apply when
determining indefiniteness. Enzo Biochem, Inc. v. Applera
Corp., 599 F.3d 1325, 1332–33 (Fed. Cir. 2010). We
therefore primarily consider the intrinsic evidence con-
sisting of the claim language, the specification, and the
prosecution history. Id. In addition, similar to claim
construction, courts may consider certain extrinsic evi-
dence in resolving disputes regarding indefiniteness.
Exxon Research & Eng’g Co., 265 F.3d at 1376 (citing
Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448, 1454 (Fed.
Cir. 1998) (en banc)); see also Verve, LLC v. Crane Cams,
Inc., 311 F.3d 1116, 1119-20 (Fed. Cir. 2002) (recognizing
that guidance as to measurement of a term of degree can
come from the intrinsic record or from the knowledge of a
person of ordinary skill in the art); Bancorp Servs., L.L.C.
v. Hartford Life Ins. Co., 359 F.3d 1367, 1375–76 (Fed.
Cir. 2004) (finding evidence not publicly available at the
time of the invention may nonetheless be probative to
show that the term was in use and had a discernible
meaning to at least some persons practicing in the field).
12                BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
In doing so, the court is not weighing evidence or making
factual findings, but rather, looking to extrinsic evidence
as part of the normal course of engaging in construction of
the patent. Exxon, 265 F.3d at 1376 (citing Cybor, 138
F.3d at 1454).
      When a “word of degree” is used, the court must de-
termine whether the patent provides “some standard for
measuring that degree.” Seattle Box Co., Inc. v. Indus.
Crating & Packing, Inc., 731 F.2d 818, 826 (Fed. Cir.
1984). Similarly, 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
. . . ).” Halliburton, 514 F.3d at 1255.
                            III.
    The disputed term “spaced relationship” does not suf-
fer from indefiniteness. Because the term was amenable
to construction, indefiniteness here would require a
showing that a person of ordinary skill would find “spaced
relationship” to be insolubly ambiguous—that it fails to
provide sufficient clarity delineating the bounds of the
claim to one skilled in the art. In this case, a skilled
artisan would find such boundaries provided in the in-
trinsic evidence.
     The district court construed “spaced relationship” to
mean that “there is a defined relationship between the
live electrode and the common electrode on one side of the
cylindrical bar and the same or a different defined rela-
tionship between the live electrode and the common
electrode on the other side of the cylindrical bar.” Summ.
J. Hr’g Tr. 10:16–22. Notwithstanding that this disputed
term was amenable to construction, the district court
determined that the term was indefinite. Specifically, the
district court stated that “a spaced relationship did not
tell me or anyone what precisely the space should be . . . .
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.             13
Not even any parameters as to what the space should be .
. . . Nor whether the spaced relationship on the left side
should be the same as the spaced relationship on the right
side.” Summ. J. Hr’g Tr. 23:3–11.
     Turning to the intrinsic evidence, the 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 be-
tween 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 independent-
ly 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 “in
physical and electrical contact with both electrodes.”).
Thus, the ’753 patent discloses certain inherent parame-
ters of the claimed apparatus, which to a skilled artisan
may be sufficient to understand the metes and bounds of
“spaced relationship.”
     The functionality of the claimed heart rate monitor as
recited in claim 1, described in the specification, and
which provided the basis for overcoming the PTO’s office
action rejections during the reexamination, sheds further
light on the meaning of “spaced relationship.” Specifical-
ly, claim 1 provides, in part:
14                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
     whereby, a first electromyogram signal will be de-
     tected between said first live electrode and said
     first common electrode, and a second electromyo-
     gram 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 dif-
     ference amplifier . . . .
    ’753 patent col. 5 ll. 48–61. This “whereby” clause de-
scribes the function of substantially removing EMG
signals that necessarily follows from the previously recit-
ed structure consisting of the elongate member, the live
electrode, and the common electrode. Id. col. 5 ll. 42–47.
Importantly, the EMG signal is detected between the live
and common electrodes, which are in “spaced relation-
ship” 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
patentability of the asserted claims upon reexamination.
J.A. 139–46. Thus, the recitation of this function in claim
1 is highly relevant in 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.”).
    The specification also describes, in part, the elec-
trodes’ “spaced relationship” in terms of their correspond-
ing function of detecting distinct electrical signals,
whereby EMG signals are substantially removed in the
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.           15
difference amplifier so that the output of the difference
amplifier substantially consists only of the ECG signal.
See, e.g., ’753 patent col. 1 ll. 53–58, col. 2 ll. 12–19.
According to Biosig, when configuring the claimed heart
rate monitor, skilled artisans can determine the “spaced
relationship” between live and common electrodes by
calculating the point in which EMG signals are substan-
tially removed.
     During reexamination, Biosig presented evidence in
support of this position in a declaration by the inventor,
Mr. Gregory Lekhtman, which was submitted in response
to a PTO office action. 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). His
declaration was based largely on tests he performed to
show the effects of electrode configuration on EMG sig-
nals measured in the palms of the users’ hands. In par-
ticular, he represented that the strength of an EMG
signal measurement is proportional to the space between
the active and ground electrode and the size of the elec-
trodes. J.A. 194–95. He further declared that it 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, according to Mr.
Lekhtman, 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. Mr. Lekhtman explained
that some of these design variables in producing a bal-
anced detection of EMG signals include spacing, size,
shape and materials of the electrodes. Moreover, Mr.
16                BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
Lekhtman represented that a common analog oscilloscope
available in 1992 would have been used by those skilled in
the art to measure the signals and to determine the best
ECG/EMG ratio. J.A. 210–11.
    For comparison, Mr. Lekhtman tested the circuitry as
recited in the ’753 patent and the circuitry as recited in
Fujisaki, the prior art cited during reexamination. Mr.
Lekhtman’s test results indicated that an ECG/EMG ratio
“in the range of about 3–10 would be manifested at the
output of the differential amplifier” of the ’753 patent as
having substantially zero influence from the EMG signal.
J.A. 213; 343. Conversely, an ECG/EMG ratio of about 1
or less, as generated by the circuitry claimed in the Fuji-
saki patent, was found to be masking the ECG signal and
thus requiring further filtering after the differential
amplifier. J.A. 213.
    Mr. Lekhtman also described Dr. Henrietta Galiana’s
test results of a laboratory mock-up of the claimed appa-
ratus—results prepared in the course of the 2004 Action
at the district court against Nautilus. J.A. 204–05; 1029–
56. Her test results and corresponding report supported
Mr. Lekhtman’s statements and demonstrated that two
detected EMG signals on opposite hands can indeed have
substantially the same amplitude and phase, and that a
difference amplifier will then reduce those EMG signals to
substantially zero. J.A. 205; 1048–54.
    Finally, extrinsic evidence underscores the intrinsic
evidence. In particular, Biosig submitted a declaration of
yet another expert, Dr. George Yanulis, in support of its
opposition to Nautilus’s summary judgment motion in the
underlying district court litigation, which confirmed Mr.
Lekhtman’s and Dr. Galiana’s test results and reports.
J.A. 1670.
    In summary, the claims provide inherent parameters
sufficient for a skilled artisan to understand the bounds of
“spaced relationship.” In addition, a skilled artisan could
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.          17
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 sub-
stantial removal of EMG signals from ECG signals while
simulating an exercise. These parameters constitute the
metes and bounds of “spaced relationship” as articulated
in the ’753 patent. Nothing more rigorous is required
under § 112, ¶ 2.
    The district court nonetheless held Biosig had not ar-
ticulated with specificity the dimensions or other parame-
ters characterizing the space between the electrodes: “It
should be half inch, one inch, two inches, three inches.
What is the space[d] relationship?” Summ. J. Hr’g Tr.
35:7–8. The district court likewise stated that the ’753
patent failed to disclose the “composition of the handle”
and whether the electrodes were “between the two middle
fingers, the outer first and fourth finger, the thumb
underneath and the fingers on top? Where is the spaced
relationship?” Summ. J. Hr’g Tr. 38:16–24. The district
court also questioned whether having “small” hands as
opposed to “large” hands would affect the “spaced rela-
tionship” between the live and common electrodes. Summ.
J. Hr’g Tr. 40:2–6. Moreover, the district court found
nothing in evidence that provided how a skilled artisan
would have determined the appropriate parameters
yielding the necessary “spaced relationship” as recited by
the ’753 patent: “[W]hat [the expert] says is that through
trial and error, which he doesn’t describe, one can find a
spaced relationship. That may be. But there’s no descrip-
tion.” Summ. J. Hr’g Tr. 39:6–8. These inquiries however
18                BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
miss the mark in this instance because they do not sup-
port an indefiniteness analysis.
     To begin, we have not insisted that claims be plain on
their face in order to avoid a determination of invalidity
for indefiniteness. Exxon, 265 F.3d at 1375. “If the mean-
ing of the claim is discernible, even though the task may
be formidable and the conclusion may be one over which
reasonable persons will disagree, we have held the claim
sufficiently clear to avoid invalidity on indefiniteness
grounds.” Id. In addition, “[p]rovided that the claims are
enabled, and no undue experimentation is required, the
fact that some experimentation may be necessary to
determine the scope of the claims does not render the
claims indefinite.” Id. at 1379. When relevant values can
be obtained, § 112 ¶ 2 is satisfied. Marley Mouldings Ltd.
v. Mikron Indus., Inc., 417 F.3d 1356, 1360–61 (Fed. Cir.
2005) (“Although the district court was concerned that the
claims encompass a range of volumes and thereby also of
weights, § 112 ¶2 is satisfied when the relevant values
can be ‘calculated or measured.’”) (citation omitted). By
embracing this standard, “we accord respect to the statu-
tory presumption of patent validity, and we protect the
inventive contribution of patentees, even when the draft-
ing of their patents has been less than ideal.” Exxon, 265
F.3d at 1375 (internal citations omitted); see Morton Int’l,
Inc. v. Cardinal Chem. Co., 5 F.3d 1464, 1470, 1472 (Fed.
Cir. 1993) (citing 35 U.S.C. § 282). Therefore, objections
relating to the mere fact that there may be some need for
experimentation to determine the scope of the claims
carry little weight.
     Likewise, the district court’s objections to the claims
as written do not support imprecision of the claims.
Rather, the objections are based on the premise that the
’753 patent does not include disclosure sufficiently com-
mensurate with the scope of the claims. These objections,
if relevant, provide grounds for invalidity under § 112, ¶ 1
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.             19
and not § 112, ¶ 2.4 As this court has explained:
   A patent claim to a fishing pole would not be inva-
   lid on indefiniteness grounds if it contained a lim-
   itation requiring that the pole be “at least three
   feet long,” even though a 50 foot long fishing pole
   would not be very practical. By the same token,
   there is nothing indefinite about the claim lan-
   guage at issue in this case simply because it co-
   vers some embodiments that may be inoperable.
    Exxon, 265 F.3d at 1382; Personalized Media
Commc’ns, LLC v. Int’l Trade Comm’n, 161 F.3d 696, 706
(Fed. Cir. 1998) (rejecting expert testimony stating gener-
ally that a “digital detector” was not adequately disclosed
in the patent and could not be built by those of ordinary
skill as relevant only to the sufficiency of the written
description to enable the practice of the invention of the
claims); Miles Labs., Inc., v. Shandon, Inc., 997 F.2d 870,
875, (Fed. Cir. 1993) (same). Breadth is not indefinite-
ness. SmithKline Beecham Corp. v. Apotex Corp., 403 F.3d
1331, 1340–41 (Fed. Cir. 2005). Hence, inquiries as to the
size of the users’ hands, placement of fingers, and the
“composition of the handle” may be relevant, if at all, to
issues that relate to enablement under § 112, ¶ 1, not
indefiniteness under § 112, ¶ 2, because they are directed
to the operability of varying embodiments of the claimed
heart rate monitor, not to the precision of the claims at



   4    35 U.S.C. § 112, ¶ 1 generally relates to the suffi-
ciency of the written descriptions of patents, including
enablement, and states in relevant part: “The specifica-
tion shall contain a written description of the invention,
and of the manner and process of making and using it, in
such full, clear, concise, and exact terms as to enable any
person skilled in the art to which it pertains . . . to make
and use the same . . . .”
20                BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
issue. Accordingly, these objections do not address the
inherent parameters set forth in the intrinsic evidence.
     Still, Nautilus seeks support in Halliburton. In Hal-
liburton, the invention at issue was a “fragile gel” that
was used in drilling. 514 F.3d at 1246–47. This court
found that the patent-at-issue did not disclose how the
claimed “fragile gel” performed differently than the dis-
closed prior art, such as “how much more quickly the gels
broke when stress was imposed, or how much more quick-
ly the gels reformed when stress was removed.” Hallibur-
ton, 514 F.3d at 1253. Halliburton’s failure to distinguish
the fragileness of the drilling fluids of the invention from
the close prior art, according to this court, was fatal
because it did not limit on what was invented beyond the
prior art. Id. For example, the court noted that the fluids
of the invention may provide less resistance to shearing
(i.e., break more quickly) than the prior art fluids, but the
degree of improved speed, the court said, remained am-
biguous. Id. Thus, this court held that it was unclear
whether a skilled artisan would have interpreted this
claim as having an upper bound of fragility. Id.
        Halliburton is distinguishable. Here, the claimed
apparatus has inherent parameters where the “spaced
relationship” cannot be larger than the width of a user’s
hand. Additionally, it has been shown that skilled arti-
sans can readily ascertain the bounds of the “spaced
relationship” through tests using standard equipment.
Thus, the “upper bound” that was lacking in Halliburton
is found here. As a result, Halliburton fails to support
Nautilus.
    Rather, this case is analogous to Star Scientific II.
There, the disputed term was “controlled environment” as
applied to the practice of tobacco curing and “whether a
person of ordinary skill would know how to establish a
controlled environment to perform the claimed method.”
Star Scientific II, 655 F.3d at 1373-74. This court held
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.           21
that the fact that the patents-at-issue did not give exact
numbers measuring humidity, temperature, and airflow
in a conventional curing barn was not dispositive. Id. at
1374. On the contrary, this court found there was evi-
dence showing that “a person of skill in the art of tobacco
curing would possess adequate understanding to manipu-
late these variables to create a controlled environment.”
Id. Further, because conventional curing varied depend-
ing on the conditions for each cure, specific numerical
values were found not necessary for one skilled in the art
to implement conventional curing. Id. Hence, “controlled
environment” was held not insolubly ambiguous.
    Like Star Scientific II, the record shows that the vari-
ables here, including the spacing, size, shape, and materi-
al affecting the “spaced relationship” between the
electrodes, can be determined by those skilled in the art.
Thus, “spaced relationship” cannot be said to be insolubly
ambiguous.
                              IV.
    Contrary to the district court’s decision and to Nauti-
lus’s contention on appeal, this court’s jurisprudence does
not proscribe drafting or defining claims in relation to
their functions. Moore U.S.A., Inc. v. Standard Register
Co., 229 F.3d 1091, 1111 (Fed. Cir. 2000) (“We note that
there is nothing wrong with defining the dimensions of a
device in terms of the environment in which it is to be
used.”); see also Vizio, Inc. v. Int’l Trade Comm’n, 605
F.3d 1330, 1340 (Fed. Cir. 2010) (“[T]he ‘for decoding’
language . . . is properly construed as a limitation, and
not merely statement of purpose or intended use for the
invention, because ‘decoding’ is the essence or a funda-
mental characteristic of the claimed invention.”). That is,
“claims are not necessarily indefinite for using functional
language.” Microprocessor Enhancement Corp. v. Texas
Instruments Inc., 520 F.3d 1367, 1375 (Fed. Cir. 2008).
Indeed, functional language in a means-plus-function
22                BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
format is explicitly authorized by statute. 35 U.S.C. § 112,
¶6. Functional language may also be used to limit the
claims without having the means-plus-function format.
Microprocessor Enhancement Corp., 520 F.3d at 1375.
    Yet, the district court found the evidence consisting of
test results and their corresponding references to “sub-
stantial removal of EMG signals” conclusory because,
according to the court, Biosig failed to show how it con-
ducted its tests that allegedly illustrate a “spaced rela-
tionship” between the electrodes and the substantial
removal of EMG signals. In particular, the district court
found fault with the experts’ references to the function of
the claim term only, and it ultimately held that “this is all
a description of the desired result and not a description of
any invention . . . and, therefore, violates the requirement
of specificity in Section 112.” Summ. J. Hr’g Tr. 42:25–
43:4.
    Courts often refer to the context in which the patent-
ed invention is claimed to ascertain its scope. Medrad,
Inc. v. MRI Devices Corp., 401 F.3d 1313, 1319 (Fed. Cir.
2005) (“It is therefore entirely proper to consider the
functions of an invention in seeking to determine the
meaning of particular claim language.”). Hence, to de-
termine the proper meaning of “spaced relationship,” we
must refer to “spaced relationship” in the context of the
intrinsic evidence, including the claim language, specifi-
cation, and prosecution history. The district court viewed
“spaced relationship” in a vacuum by choosing to turn a
blind eye to the functional aspects of claim 1, e.g., how
“spaced relationship” contributes to the removal of noise
signals, such as EMG signals, and the overall capabilities
of the claimed heart rate monitor. However, without
context, it would be impossible to ascertain “what the
inventors actually invented and intended to envelop with
the claim,” Renishaw PLC v. Marposs Societa’ per Azioni,
158 F.3d 1243, 1250 (Fed. Cir. 1998), and to examine the
patent from the perspective of a person skilled in the art,
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.             23
e.g., Tegal Corp. v. Tokyo Electron Am., Inc., 257 F.3d
1331, 1342 (Fed. Cir. 2001). Thus, to the extent the
district court failed to consider Biosig’s evidence based on
its reasoning that the evidence spoke only to the “function
of the claim,” this was error.
    Nautilus makes a related contention that the claims
at issue are invalid as they impermissibly claim both an
apparatus and a method of use. Specifically, Nautilus
contends that claim 1 recites a heart rate monitor and a
required step that a user holds the monitor. According to
Nautilus, it is unclear whether the alleged infringement
occurs when one makes a heart rate monitor having the
recited structural elements, or whether infringement
allegedly occurs when the user actually holds the handle
and contacts the electrodes. This contention is unpersua-
sive.
     The ’753 patent recites apparatus claims with func-
tional limitations that describe the capability of substan-
tially removing EMG signals. See, e.g., ’753 patent col. 5 l.
16–col. 6 l. 15. Indeed, claim 1 of the ’753 patent is clearly
limited to a heart rate monitor possessing the recited
structure that is capable of substantially removing EMG
signals. It is not indefinite. Accordingly, this case fails to
invoke our decision in IPXL Holdings, LLC v. Ama-
zon.com, Inc., 430 F.3d 1377 (Fed. Cir. 2005) (holding
claims at issue as indefinite because they simultaneously
claimed an apparatus and method steps).
                        CONCLUSION
    The only issue on this appeal is the summary judg-
ment of indefiniteness. Other aspects of the defense of
patent invalidity, although raised in the district court, are
not before us, and may be considered on remand. We
reverse the district court’s invalidity determination and
remand for further proceedings.
            REVERSED AND REMANDED
  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.
                 ______________________

SCHALL, Circuit Judge, concurring.
    I join the court’s reversal of the judgment on appeal
and its remand of the case for further proceedings. I
write separately, however, because, while I agree with the
court that the district court erred in holding claims 1 and
11 of the ’753 patent invalid by reason of indefiniteness, I
would rest that ruling on a more limited analysis. I
therefore respectfully concur.
     In Part II of the Discussion section of its opinion, the
court correctly sets forth our law on indefiniteness. In
short, a claim is indefinite (1) when it is not amenable to
construction or (2) when, even if it can be construed, “the
construction remains insolubly ambiguous, meaning it
fails to provide sufficient clarity [delineating the metes]
2                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
and bounds of the claim to one of skill in the art,” Star
Scientific, Inc. v. R.J. Reynolds Tobacco Co., 655 F.3d
1364, 1373 (Fed. Cir. 2011). See Datamize, LLC v.
Plumtree Software, Inc., 417 F.3d 1342, 1347 (Fed. Cir.
2005) (“Only claims ‘not amenable to construction’ or
‘insolubly ambiguous’ are indefinite.”); see also Star
Scientific, Inc. v. R.J. Reynolds Tobacco Co., 537 F.3d
1357, 1371 (Fed. Cir. 2008) (“In and of itself, a reduction
of the meaning of a claim term into words is not disposi-
tive of whether the term is definite . . . . And if reasona-
ble efforts at claim construction result in a definition that
does not provide sufficient particularity and clarity to
inform skilled artisans of the bounds of the claim, the
claim is insolubly ambiguous and invalid for indefinite-
ness.”) (internal citations omitted). As the court con-
cludes, neither of these two grounds for indefiniteness
exists in this case.
    First, the “spaced relationship” limitation plainly was
amenable to construction. The district court construed
the two recitations of “in spaced relationship with each
other” in claim 1 to mean that “there is a defined relation-
ship between the live electrode and the common electrode
on one side of the cylindrical bar and the same or a differ-
ent defined relationship between the live electrode and
the common electrode on the other side of the cylindrical
bar.” See Biosig Instruments, Inc. v. Nautilus, Inc., No.
10-cv-7722, slip op. at 3 (S.D.N.Y. Sept. 29, 2011) (Dkt.
32, “Summary Order Memorializing Court’s Patent Claim
Term Constructions After a Markman Hearing”). Neither
Biosig nor Nautilus disputes that the district court did, in
fact, construe the “spaced relationship” limitation.
    Second, the court’s construction provided sufficient
clarity to one of skill in the art as to the metes and bounds
of the “spaced relationship” limitation. Put most simply,
the district court construed that limitation to require
“defined relationships,” between the live electrode and the
 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.           3
common electrode on each side of the cylindrical bar. 1
What that construction means is that, on each side of the
cylindrical bar, there is a fixed spatial relationship be-
tween the live electrode and the common electrode. And
the court correctly states that the intrinsic evidence
relating to the ’753 patent “discloses certain inherent
parameters of the claimed apparatus, which to a skilled
artisan may be sufficient to understand the metes and
bounds of ‘spaced relationship’.” See Majority Op. at 13.
In my view, along with the court’s subsequent rejection of
Nautilus’s reliance on Halliburton Energy Services, Inc. v.
M-I LLC, 514 F.3d 1244 (Fed. Cir. 2008); and IPXL Hold-
ings, L.L.C. v. Amazon.com, Inc., 430 F. 3d 1377 (Fed. Cir.
2005), that is all that is needed to put this case to rest.
    My concern with the balance of the court’s analysis is
that it presumes a functional linkage between the “spaced
relationship” limitation and the removal of EMG signals.
In other words, the analysis proceeds as if the “spaced
relationship” limitation itself—rather than other limita-
tions of claim 1—included a functional requirement to
remove EMG signals. See Majority Op. at 16–17 (“[A]
skilled artisan could apply a test and determine the
‘spaced relationship’ as pertaining to the function of
substantially removing EMG signals.”); id. at 13 (“The
functionality of the claimed heart rate monitor as recited
in claim 1, described in the specification, and which
provided the basis for overcoming the PTO’s office action
rejections during reexamination, sheds further light on
the meaning of ‘spaced relationship.’”). Indeed, the par-
ties to this appeal and the district court seem to presume
the same. The language of the “spaced relationship”


   1    Although this construction may be seen as broad,
as the court notes, “[b]readth is not indefiniteness.” See
Majority Op. at 19 (citing SmithKline Beecham Corp. v.
Apotex Corp., 403 F.3d 1331, 1340–41 (Fed. Cir. 2005)).
4                 BIOSIG INSTRUMENTS, INC.   v. NAUTILUS, INC.
limitation, however, does not contain a functional re-
quirement:
    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 elec-
    trode mounted on said second half in spaced rela-
    tionship with each other
’753 patent col. 5 ll. 28–33. In addition, as seen above, the
district court’s construction of the “spaced relationship”
limitation does not include any functional language
related to the removal of EMG signals, and Nautilus has
not conditionally cross-appealed that construction.
    In my view, we should not address a functional limita-
tion included neither in the “spaced relationship” limita-
tion itself nor in the district court’s construction of that
limitation. By allowing the functional limitation of EMG
removal from elsewhere in claim 1 to color our analysis of
the definiteness of the “spaced relationship” limitation, it
seems to me we address an issue that is not currently
before us.
