  United States Court of Appeals
      for the Federal Circuit
              __________________________

                DEERE & COMPANY,
                 Plaintiff-Appellant,
                           v.
                  BUSH HOG, LLC,
              Defendant-Cross Appellant,
                          AND

        GREAT PLAINS MANUFACTURING
               INCORPORATED,
            Defendant-Cross Appellant.
              __________________________

                2011-1629, -1630, -1631
              __________________________

   Appeal from the United States District Court for the
Southern District of Iowa in Case No. 09-CV-0095, Senior
Judge Charles R. Wolle.
             ___________________________

              Decided: December 4, 2012
             ___________________________

    RODERICK R. MCKELVIE, Covington & Burling LLP, of
Washington, DC, argued for plaintiff-appellant. With him
on the brief was R. JASON FOWLER.

    CRAIG C. MARTIN, Jenner & Block LLP, of Chicago, Il-
linois, argued for defendant-cross appellant Bush Hog,
DEERE & CO   v. BUSH HOG                               2


LLC. With him on the brief were STEVEN R. TRYBUS, of
Chicago, Illinois, MATTHEW S. HELLMAN, of Washington,
DC, and ELIZABETH A. EDMONDSON, of New York, New
York. Of counsel were JEFFREY D. HARTY and EDMUND J.
SEASE, McKee, Voorhees & Sease, P.L.C., of Des Moines,
Iowa.

    SCOTT R. BROWN, Hovey Williams LLP, of Overland
Park, Kansas, argued for defendant-cross appellant Great
Plains Manufacturing Incorporated. With him on the brief
was MATTHEW B. WALTERS.
              __________________________

Before RADER, Chief Judge, NEWMAN and PLAGER, Circuit
                       Judges.
RADER, Chief Judge.
     The United States District Court for the Southern
District of Iowa construed the terms of Deere & Co.’s
(“Deere”) U.S. Patent No. 6,052,980 (the “’980 Patent”)
and granted Bush Hog, LLC’s (“Bush Hog”) and Great
Plains Manufacturing, Inc.’s (“Great Plains”) motions for
summary judgment of noninfringement.          This court
affirms the construction of “rotary cutter deck” and the
determination that the terms “substantially planar” and
“easily washed off” do not render the asserted claims
invalid under 35 U.S.C. § 112. Because the district erro-
neously construed the term “into engagement with” to
require direct contact, this court vacates that construc-
tion, reverses the grant of summary judgment, and re-
mands for further proceedings.
                           I.
     The ’980 Patent discloses an “easy clean dual wall
deck” for a rotary cutter.    Bush Hog and Great Plains
(collectively, “Defendants”), manufacture rotary cutters
3                                    DEERE & CO   v. BUSH HOG


that are pulled behind a tractor and used to mow wide
swaths of ground. The accused rotary cutters can “rough
cut” fields after a harvest or clear weeds and brush along
roadsides. The ’980 Patent addresses a problem encoun-
tered by rotary cutters: “[d]uring cutting/shredding of
material, such as cotton[,] corn, milo and wheat stubble,
grass, etc. with a rotary cutter, debris accumulates on the
top of the cutter deck. If not regularly cleaned off, the
debris retains moisture which eventually results in the
deck rusting out.” ’980 Patent, col. 1, ll. 21–25.
     The specification explains that prior art rotary cutters
had structural components such as gearboxes and deck
bracings mounted either on top of or underneath the
cutter deck. Id. col. 1, ll. 25–35. When placed on top of
the deck, these components create traps for debris and
water, making it difficult to clean the deck. Id. When
placed underneath the deck, the structural components
interfere with the flow of cut material, reducing cutting
efficiency. Id.
    The ’980 Patent discloses a dual-wall deck that en-
closes the structural components in a torsionally-strong
box. This leaves smooth surfaces on the top and bottom of
the deck. Figure 3 of the ’980 Patent shows a side view of
the claimed dual-wall deck. In the embodiment shown,
the front and rear of the upper deck wall 56 slope down to
contact the lower deck wall 28. Id. col. 2, l. 59 – col. 3, l.
4.
DEERE & CO   v. BUSH HOG                                  4


’980 Patent, fig. 3 (highlighting added).
    Claim 1 of the ’980 Patent recites:
    1. A rotary cutter deck comprising:
      a lower, substantially planar, horizontal deck
        wall;
      an upper deck wall including a central portion
        elevated above said lower deck wall, and
      front and rear portions respectively sloped
        downwardly and forwardly, and downwardly
        and rearwardly from said central portion
        into engagement with, and being se-
        cured to, said lower deck wall;
      and right- and left-hand end wall structures re-
        spectively being joined to right- and left-hand
        ends of said lower and upper deck walls to
        thereby define a box section having torsional
        stiffness.
    Id. col. 4, ll. 44–53 (emphasis added).
    The district court construed the term “into engage-
ment with” to mean “brought into contact with,” and
construed “being secured to” as “fastened or attached.”
Deere & Co. v. Bush Hog LLC (“Claim Construction
Order”), No. 3:09-cv-95 (S.D. Iowa Jan. 25, 2011). The
district court granted summary judgment of noninfringe-
ment, holding Deere did not raise a genuine issue of
material fact as to literal infringement because “the upper
deck walls do not come into contact with the lower deck
walls in any of the accused products.” Deere & Co. v.
Bush Hog LLC (“Summary Judgment Opinion”), No. 3:09-
cv-95, slip. op. at 13 (S.D. Iowa Aug. 1, 2011).
    In each of the accused products, an intermediate
structure connects the upper deck wall to the lower deck
5                                    DEERE & CO   v. BUSH HOG


wall at both the front and rear portions of the deck. Id. at
3. Like the district court, this court refers to those inter-
mediate structures as “connectors.” The size and shape of
the connectors is different in the various accused prod-
ucts, but the district court did not distinguish between
different types of connectors in granting summary judg-
ment. The differences are therefore irrelevant to this
appeal.
    In addition to granting summary judgment of no lit-
eral infringement, the district court held Deere could not
assert infringement under the doctrine of equivalents
because doing so would vitiate the “into engagement with”
limitation. Id. at 15–16. Further, the district court
barred Deere from asserting equivalence because the “into
engagement with” limitation “specifically excludes struc-
tures where the deck walls are not engaged with each
other.” Id. at 16.
   The district court entered final judgment in favor of
Defendants, dismissing without prejudice Defendants’
counterclaims of invalidity. This court has jurisdiction
under 28 U.S.C. § 1295(a)(1).
                             II.
    This court reviews claim construction without defer-
ence. Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448,
1455–56 (Fed. Cir. 1998) (en banc). This court also re-
views a district court’s grant of summary judgment with-
out deference. ICU Med., Inc. v. Alaris Med. Sys. Inc., 558
F.3d 1368, 1374 (Fed. Cir. 2009).
    The district court erroneously construed the term
“into engagement with” to require direct contact between
the upper and lower deck walls. At the outset, the claim
language itself counsels against this narrow interpreta-
tion of the term. “[T]he words of a claim ‘are generally
DEERE & CO   v. BUSH HOG                                    6


given their ordinary and customary meaning’ . . . that the
term would have to a person of ordinary skill in the art in
question at the time of the invention.” Phillips v. AWH
Corp., 415 F.3d 1303, 1312–13 (Fed. Cir. 2005) (en banc)
(quoting Vitronics Corp. v. Conceptronic, Inc., 90 F.3d
1576, 1582 (Fed. Cir. 1996)). “[T]he person of ordinary
skill in the art is deemed to read the claim term not only
in the context of the particular claim in which [it] ap-
pears, but in the context of the entire patent, including
the specification.” Id. at 1313. While claim terms are
understood in light of the specification, a claim construc-
tion must not import limitations from the specification
into the claims. Id. at 1323.
    Claim 1 of the ’980 Patent requires the front and rear
of the upper deck wall to slope downwardly “into engage-
ment with, and being secured to,” the lower deck wall.
’908 Patent, col. 4, l. 49. To give effect to all terms of the
claim, “secured to” and “into engagement with” must have
distinct meanings. See Bicon, Inc. v. Straumann Co., 441
F.3d 945, 950 (Fed. Cir. 2006). The parties agree that two
objects may be “secured to” one another without being in
direct contact. For example, a rigid bracket can “secure”
two objects together yet maintain space between them.
Defendants argue that if “engagement” also includes
connection through indirect contact, then it is redundant
with “secured to.”
    This court gives effect to the claim terms “secured to”
and “engagement” as conveying distinct meanings. The
term “engagement” connotes a connection between two
objects in which the motion of one object is constrained by
the other. This connection can be indirect, such as where
a motor is engaged with a gear through a second, inter-
mediate gear. The gear and motor are engaged even
though they are not “secured” together, such as with nuts
and bolts or by welding. Objects that are secured to one
7                                   DEERE & CO   v. BUSH HOG


another are not just connected, but are fastened or at-
tached in some way. Thus, construing “engagement” to
include indirect contact, consistent with its plain mean-
ing, does not render the term superfluous.
    The specification illustrates that “engagement” in-
cludes indirect contact between the upper and lower deck
walls. As shown in Figure 1, the “[o]uter rear portions of
the right- and left-hand upper deck wall sections 56 and
58 [yellow] are connected to the right- and left-hand lower
deck wall portions [red] by respective downwardly and
rearwardly inclined filler plates 86 and 88 [blue].” ’980
Patent, col. 3, ll. 4–7 (highlighting added) (upper deck
wall section 58 not labeled; filler plate 86 not shown).
Thus, the filler plates provide an indirect connection by
which the upper deck wall slopes “downwardly and rear-
wardly . . . into engagement with” the lower deck wall.




’980 Patent, Fig. 1 (highlighting added).
    Defendants respond that the filler plates cannot be
considered to bring the upper deck “into engagement
with” the lower deck as contemplated by Claim 1, because
they are located at a point where the upper deck is sub-
stantially horizontal. Claim 1 requires engagement at a
DEERE & CO   v. BUSH HOG                                   8


point where the upper deck “slope[s] downwardly” to meet
the lower deck. Id. col. 4, ll. 45–50. However, the specifi-
cation describes the portion of the upper deck wall where
the filler plate is attached (labeled 64 in Figure 1) as
“convexly bowed from front to rear.” Id. col. 2, ll. 44–53.
In other words, the upper deck wall is “sloped down-
wardly” at the point where it engages the lower deck wall
via the filler plate.
     Claim 1 indicates that the “engagement” between the
upper and lower deck walls serves to impart “torsional
stiffness” to the rotary cutter deck. Id. col. 4, ll. 44–53.
The specification depicts this torsional stiffness in a way
that does not require direct contact between the upper
and lower deck walls. Specifically, the specification
explains that upper and lower decks are “joined together
to create a central box structure having good torsional
strength.” Id. col. 1, ll. 60–64. Elsewhere, the specifica-
tion states that “the upper and lower deck walls . . .
cooperate with each other, the filler plates, and [other
structures] to form a box section having torsional rigid-
ity.” Id. col. 4, ll. 28–32.
    The ordinary meanings of the terms that describe the
relationship between the upper and lower deck walls—
“cooperate,” “join[ ],” “engage[ ]”—do not necessitate direct
contact. Further, the filler plates, which indirectly con-
nect the upper and lower deck walls, are expressly de-
scribed as forming part of the torsionally-strong box
structure. In other words, the specification contemplates
the upper deck wall engaging the lower deck wall by way
of the filler plates to achieve the desired torsional
strength. Read in the context of the specification, Claim 1
allows for the upper deck wall to come “into engagement
with” the lower deck wall through indirect contact.
9                                   DEERE & CO   v. BUSH HOG


     The district court granted summary judgment of non-
infringement because the upper and lower deck walls of
the accused products do not directly contact one another.
Because in the context of the ’980 Patent “into engage-
ment with” encompasses indirect contact, this court
vacates the district court’s construction of this term,
reverses the grant of summary judgment, and remands
for further proceedings.
                           III.
    The district court held Deere could not assert in-
fringement under the doctrine of equivalents because the
“into engagement with” limitation, as construed by the
court, “is binary in nature”—either the upper deck wall is
“in contact with the lower deck wall or it is not.” Sum-
mary Judgment Opinion, slip. op. at 15 (internal quota-
tion omitted). Further, the court held Deere’s theory of
equivalence was precluded by the doctrine of specific
exclusion, “because the ‘into engagement with’ claim
limitation specifically excludes structures where the deck
walls are not engaged with each other.” Id. at 16. Be-
cause the district court’s analysis of this issue was based
on its erroneous claim construction, this court also va-
cates the grant of summary judgment of no infringement
under the doctrine of equivalents.
     The district court’s treatment of the doctrine of
equivalents reveals a common misperception regarding
“vitiation” that warrants some discussion. The concept of
vitiation derives from the requirement that the doctrine of
equivalents must be applied to the claims “on an element-
by-element basis,” so that every claimed element of the
invention—or its equivalent—is present in the accused
product. Warner-Jenkinson Co. v. Hilton Davis Chem.
Co., 520 U.S. 17, 40 (1997). Of course, in every case
applying the doctrine of equivalents, at least one claimed
DEERE & CO   v. BUSH HOG                                  10


element is not literally present in the accused product.
The question is “whether an omitted part is supplied by
an equivalent device or instrumentality.” Id. at 32 (quot-
ing Hubbell v. United States, 179 U.S. 77 (1900)). Thus,
the doctrine of equivalents, by its very nature, assumes
that some element is missing from the literal claim lan-
guage but may be supplied by an equivalent substitute.
    The test of the equivalence of a proposed substitute
for a missing element is ordinarily a factual inquiry
reserved for the finder of fact. Warner-Jenkinson, 520
U.S. at 38–39; Sage Prods., Inc. v. Devon Indus., Inc., 126
F.3d 1420, 1423 (Fed. Cir. 1997). It is the role of the
court, however, to ensure that the doctrine of equivalents
is not permitted to overtake the statutory function of the
claims in defining the scope of the patentee’s exclusive
rights. Sage, 126 F.3d at 1424. Thus, for example, courts
properly refuse to apply the doctrine of equivalents
“where the accused device contain[s] the antithesis of the
claimed structure.” Planet Bingo, 472 F.3d at 1345. In
such a case, application of the doctrine of equivalents
would “vitiate” a claim element. Warner-Jenkinson, 520
U.S. at 39 n.8.
     “Vitiation” is not an exception to the doctrine of
equivalents, but instead a legal determination that “the
evidence is such that no reasonable jury could determine
two elements to be equivalent.” Id. The proper inquiry
for the court is to apply the doctrine of equivalents, asking
whether an asserted equivalent represents an “insubstan-
tial difference” from the claimed element, or “whether the
substitute element matches the function, way, and result
of the claimed element.” Id. at 40. If no reasonable jury
could find equivalence, then the court must grant sum-
mary judgment of no infringement under the doctrine of
equivalents. Id. at 39 n.8.
11                                  DEERE & CO   v. BUSH HOG


    Courts should be cautious not to shortcut this inquiry
by identifying a “binary” choice in which an element is
either present or “not present.” Stated otherwise, the
vitiation test cannot be satisfied by simply noting that an
element is missing from the claimed structure or process
because the doctrine of equivalents, by definition, recog-
nizes that an element is missing that must be supplied by
the equivalent substitute. If mere observation of a miss-
ing element could satisfy the vitiation requirement, this
“exception” would swallow the rule. And, the Supreme
Court declined to let numerous contentions bury the
doctrine. Id. at 21, 40. Thus, preserving the doctrine in
its proper narrowed context requires a court to examine
the fundamental question of whether there is a genuine
factual issue that the accused device, while literally
omitting a claim element, nonetheless incorporates an
equivalent structure.
    In this case, the district court construed “contact” to
require “direct contact,” and thus found that allowing “no
direct contact” would vitiate the court’s construction. Yet,
a reasonable jury could find that a small spacer connect-
ing the upper and lower deck walls represents an insub-
stantial difference from direct contact. See TurboCare
Div. of Demag Delaval Turbomachinery Corp. v. Gen.
Elec. Co., 264 F.3d 1111, 1124 (Fed. Cir. 2001) (construing
claim term “contact” to require “touching” but remanding
question of whether “indirect contact” could be equiva-
lent). Thus, the trial court erred by invoking the vitiation
exclusion in this context.
    This court has considered Defendants’ other argu-
ments against application of the doctrine of equivalents,
but finds them unpersuasive. This court vacates the
district court’s determination that Deere is barred from
asserting infringement under the doctrine of equivalents.
DEERE & CO   v. BUSH HOG                                  12


                            IV.
    This court will take the opportunity to streamline this
case by addressing the additional claim construction
arguments raised in this appeal. See Thorner v. Sony
Computer Entm’t Am. LLC, 669 F.3d 1362, 1369 (Fed. Cir.
2012); Advanced Software Design Corp. v. Fiserv, Inc., 641
F.3d 1368, 1378 (Fed. Cir. 2011); Riverwood Int’l Corp. v.
R. A. Jones & Co., 324 F.3d 1346, 1357 (Fed. Cir. 2003)
(addressing appellee’s challenge to claim construction
because judgment of invalidity in appellee’s favor was
vacated). The district court’s claim constructions have
been fully briefed on appeal and may become important
on remand.
    Deere appeals the construction of “rotary cutter deck,”
which the district court defined as “the blade housing on a
power mower.” Claim Construction Order, slip op. at 1.
The district court rejected Deere’s proposed construction,
which would have excluded “consumer turf care equip-
ment, self-powered mowers, self-propelled mowers or
walk-behind mowers.” Id. Deere seeks to exclude such
consumer lawn mowers to limit the scope of prior art that
may be asserted against the ’980 Patent.
    The term “rotary cutter deck” appears only in the pre-
amble of the asserted claims, although it provides antece-
dent basis for “said deck” in Claim 5. As a preliminary
matter, this court must determine whether the term is a
limitation of the claims. Whether to treat a preamble as a
limitation is “determined on the facts of each case in light
of the overall form of the claim, and the invention as
described in the specification and illuminated in the
prosecution history.” Applied Materials, Inc. v. Advanced
Semiconductor Materials Am., Inc., 98 F.3d 1563, 1572–73
(Fed. Cir. 1996). In general, a preamble is limiting if it is
“‘necessary to give life, meaning, and vitality’ to the
13                                   DEERE & CO   v. BUSH HOG


claim.” Pitney Bowes, Inc. v. Hewlett-Packard Co., 182
F.3d 1298, 1305 (Fed. Cir. 1999) (quoting Kropa v. Robie,
187 F.2d 150, 152 (CCPA 1951)).
    In Catalina Marketing International, Inc. v. Coolsav-
ings.com, Inc., 289 F.3d 801, 808–09 (Fed. Cir. 2002), this
court identified several guideposts to determine whether a
preamble limits claim scope. Relevant here, “when recit-
ing additional structure . . . underscored as important by
the specification, the preamble may operate as a claim
limitation.” Id. at 808. Additionally, a preamble phrase
that provides antecedent basis for a claim limitation
generally limits the scope of the claim. Id. at 808; Bell
Commc’ns Research, Inc. v. Vitalink Commc’ns Corp., 55
F.3d 615, 620 (Fed. Cir. 1995). By contrast, if the body of
the claim describes a structurally complete invention, a
preamble is not limiting where it “merely gives a name” to
the invention, extols its features or benefits, or describes a
use for the invention. Catalina, 289 F.3d at 809.
     The recitation of a “rotary cutter deck” in Claim 1 is
necessary to understand the subject matter encompassed
by the claim, which otherwise generally recites deck walls
that “define a box section having torsional stiffness.” ’980
Patent, col. 4, ll. 44–53. Unlike non-limiting preamble
terms, “rotary cutter deck” does not merely state a name
or a use for the claimed box section. Rather, the term
describes a “fundamental characteristic of the claimed
invention” that informs one of skill in the art as to the
structure required by the claim. Poly-Am., L.P. v. GSE
Lining Tech., Inc., 383 F.3d 1303, 1310 (Fed. Cir. 2004).
For example, that the claim is drawn to a “rotary cutter
deck” informs the meaning of the “torsional stiffness”
limitation—the claimed structure must possess sufficient
stiffness to withstand the torsional loads imposed by the
operation of a rotary cutter.
DEERE & CO   v. BUSH HOG                                   14


    The specification further demonstrates that the pre-
amble phrase “rotary cutter deck” is a limitation. The
specification repeatedly refers to the “present invention”
as “an improved deck for a rotary cutter,” or a “rotary
cutter deck.” ’980 Patent, col. 1, ll. 19–55. The title of the
patent, the summary of the invention, and every drawing
describe the invention as a deck for a rotary cutter. See
Poly-Am., 383 F.3d at 1310. The specification explains
that the invention addresses a concern specific to rotary
cutters: the need for a cutter deck that is smooth and
easy to clean, but does not reduce cutting efficiency. ’980
Patent, col. 1, ll. 19–35. In sum, the specification under-
scores the importance of “rotary cutter deck” as a limita-
tion of the claimed invention.
    Recognizing that the term is a claim limitation, this
court affirms the district court’s construction of “rotary
cutter deck” as “the blade housing on a power mower.”
The specification gives no indication that the patentee
intended to exclude “consumer turf care equipment, self-
powered mowers, self-propelled mowers or walk-behind
mowers” from the definition of “rotary cutter” as Deere
now seeks. The specification describes cutting grass with
a rotary cutter, id. col. 1, ll. 21–23, and explains that
while the disclosed embodiment shows a large rotary
cutter that supports three mower spindles, the dual wall
deck can also be made for a smaller “single spindle”
device, id. col. 4, ll. 39–42. Although the disclosed em-
bodiment has hitch supports and mounting holes that
permit it to be attached or mounted to a tractor, id. col. 3,
ll. 50–52, those structures are not required by every
asserted claim, see id. col. 4, ll. 44–67. The specification
does not limit the term rotary cutter to a device that is
mounted to a tractor, and this court will not import limi-
tations from the sole embodiment described in the specifi-
15                                   DEERE & CO   v. BUSH HOG


cation. Phillips v. AWH Corp., 415 F.3d 1303, 1323 (Fed.
Cir. 2005) (en banc).
    Moreover, during prosecution, the examiner rejected
claims as anticipated or obvious over prior art mower
decks that would be excluded from Deere’s proposed
construction. Deere did not argue that the cited refer-
ences did not disclose a “rotary cutter deck” or should be
considered non-analogous art. The prosecution history
thus provides no evidence of the clear and unmistakable
disclaimer required to limit the ordinary meaning of the
term “rotary cutter deck.”
    Defendants cross-appeal the district court’s determi-
nation that the “substantially planar” limitation of Claim
1 and the “easily . . . washed off” limitation of Claim 6 do
not render the claims invalid under 35 U.S.C. § 112 ¶ 2.
See Claim Construction Order, slip. op. at 2. A claim is
invalid as indefinite only where it is “not amenable to
construction” or is “insolubly ambiguous.” Datamize, LLC
v. Plumtree Software, Inc., 417 F.3d 1342, 1347 (Fed. Cir.
2005). Because the disputed terms do not render the
claims indefinite, this court affirms.
     The district court did not interpret “substantially pla-
nar,” finding the plain meaning sufficient. Claim Con-
struction Order, slip. op. at 1. Defendants assert the term
is insolubly ambiguous in the context of the ’980 Patent
because the claims and the specification do not explain
the term, and statements in the prosecution history
contradict its plain meaning. During prosecution, Deere
added the “substantially planar” language to distinguish
its claimed rotary cutter deck from one disclosed in U.S.
Patent No. 4,724,660 (“Bowie”). Bowie discloses a dual
deck wall with the cross-section shown in Figure 9 below.
The lower deck is highlighted in yellow.
DEERE & CO   v. BUSH HOG                                    16




Bowie, fig. 9 (highlighting added).
     This court has repeatedly confirmed that relative
terms such as “substantially” do not render patent claims
so unclear as to prevent a person of skill in the art from
ascertaining the scope of the claim. Ecolab, Inc. v. Envi-
rochem, Inc., 264 F.3d 1358, 1367 (Fed. Cir. 2001); An-
drew Corp. v. Gabriel Elecs. Inc., 847 F.2d 819, 821 (Fed.
Cir. 1988) (“The criticized words [‘approach each other,’
‘close to,’ ‘substantially equal,’ and ‘closely approximate’]
are ubiquitous in patent claims. Such usages, when
serving reasonably to describe the claimed subject matter
to those of skill in the field of the invention, and to distin-
guish the claimed subject matter from the prior art, have
been accepted in patent examination and upheld by the
courts.”).
     This court does not agree with Defendants that the
lower deck wall of Bowie is necessarily within the ordi-
nary meaning of “substantially planar.” Bowie’s lower
deck wall significantly deviates from planarity, both at
the central peak 112 and the depressions at each outer
side 117, 123. There is ample room to design lower deck
walls that are more planar than that disclosed by Bowie.
Thus, the prosecution history does not render “substan-
tially planar” nonsensical in the context of the ’980 Pat-
17                                  DEERE & CO    v. BUSH HOG


ent. To the contrary, the distinction that the lower deck
wall of Bowie is not substantially planar assists the
person of ordinary skill in the art in determining the
scope of the claims. Because “substantially planar”
reasonably describes the claimed subject matter to one
skilled in the art, it does not render Claim 1 indefinite.
    The district court did not interpret any language of
Claim 6, and found its terms not ambiguous. Claim 6
recites:
     The rotary cutter deck defined in claim 1 wherein
     said lower and upper deck walls cooperate to pre-
     sent an upwardly facing deck surface which is
     smooth and substantially obstruction free
     from front to back, whereby material may slide
     or easily be washed off said deck surface, and
     water will run off said deck surface.
’980 Patent, col. 5, ll. 5–10 (emphases added).
     On appeal, Defendants argue that the subjective term
“easily” renders Claim 6 indefinite. The specification and
prosecution history, however, provide several physical
characteristics that guide the determination of whether a
deck is “easily . . . washed off” within the meaning of
Claim 6. The specification explains that an easily cleaned
deck has “an upper, generally convex smooth surface from
which debris tends to slide off and water will run off.”
’980 Patent, col. 1, ll. 40–46. Deere reinforced this re-
quirement during prosecution, explaining it is “impor-
tant” that the front and rear portions of the upper deck be
sloped downwardly from the central section to aid the
shedding of water and debris. Response to Office Action
dated Aug. 23, 1999 in U.S. App. No. 09/118,591, at 3.
Thus, consistent with the language of Claim 6, the intrin-
sic evidence explains that a deck with a smooth, generally
convex upper surface is “easily” washed off.
DEERE & CO   v. BUSH HOG                                  18


    Moreover, the specification explains that upper decks
that “can be cleaned of debris quite easily and efficiently”
were known in the prior art. ’980 Patent, col. 1, ll. 29–31.
The availability of known easy-clean decks provides a
standard for measuring the scope of Claim 6. See Hearing
Components, Inc. v. Shure Inc., 600 F.3d 1357, 1367 (Fed.
Cir. 2010); Datamize, 417 F.3d at 1351. Contrary to
Defendants’ arguments, the ’980 Patent does not require
the deck to be more easily cleaned than prior art decks.
Rather, the invention is distinguished from prior art easy-
clean decks because it avoids mounting equipment under-
neath the deck in a manner that reduces cutting effi-
ciency. Id. col. 1, ll. 29–35 & ll. 40–42. This court affirms
the district court’s conclusion that Claim 6 is not rendered
indefinite by the relative term “easily . . . washed off.”
                             V.
     This court affirms the district court’s construction of
“rotary cutter deck” and its determination that “substan-
tially planar” and “easily . . . washed off” do not render
the claims indefinite under 35 U.S.C. § 112. Because the
district court erred by construing “into engagement with”
to require direct contact, this court vacates that construc-
tion, reverses the grant of summary judgment of nonin-
fringement, and remands for further proceedings.
    AFFIRMED-IN-PART, REVERSED-IN-PART,
      VACATED-IN-PART AND REMANDED.
