688 F.2d 1242
216 U.S.P.Q. 749
OMARK INDUSTRIES, INC., Plaintiff-Appellee,v.TEXTRON, INC., Defendant-Appellant.
No. 79-4544.
United States Court of Appeals,Ninth Circuit.
Argued and Submitted March 2, 1981.Decided Sept. 27, 1982.

John M. Webb, Webb, Burden, Robinson & Webb, Pittsburgh, Pa., for defendant-appellant.
Kenneth S. Klarquist, Klarquist, Sparkman, Campbell, Leigh, Hall & Winston, Portland, Or., for plaintiff-appellee.
Appeal from the United States District Court for the District of Oregon.
Before ANDERSON and CANBY, Circuit Judges, and CRAIG,* District Judge.
J. BLAINE ANDERSON, Circuit Judge:


1
Omark, as assignee of the Graversen patent (U.S. Patent No. 3,929,049), initiated this action against Textron alleging infringement of the assigned patent.  Textron answered by denying infringement and counterclaimed alleging the invalidity of the patent.  The parties stipulated to have the case tried before United States Magistrate George E. Juba.  In a written opinion, which constituted the findings of fact and conclusions of law as required by Fed.  R. Civ. P. 52(a), Magistrate Juba determined that claims 2 through 4 of the patent were valid and infringed.  Thereupon, the district court, Judge Otto R. Skopil presiding, entered judgment enjoining Textron's infringement and finding that Omark was entitled to an accounting to determine its damages and its right to attorneys' fees and interest.  Textron's counterclaim was dismissed.  The injunction and accounting were stayed pending the outcome of this appeal.  The district court had jurisdiction pursuant to 35 U.S.C. § 281 and 28 U.S.C. § 1338(a).  The primary issues raised by Textron on appeal are whether the district court properly found the patent infringed and whether the district court erred in failing to find the patent invalid for obviousness.  We affirm.

I. FACTUAL BACKGROUND

2
The subject matter of the patent in suit is a saw chain for use on power chain saws.  Chain saws came into popular use in the late 1940's and early 1950's.  In the early 1960's, consumer chain saws arrived on the market.  These saws were more lightweight, less expensive, and of lower horsepower than the commercial saws of the day.  It is the design of the chain for such a consumer saw that is the subject of this appeal.


3
A typical saw chain consists of drive links, cutting links and tie straps which hold the two links together.1  The cutting link is the key link in the operation of a chain saw.  It has a base portion which includes two rivet openings for connecting it to the adjoining drive links.  The base rides on the chain saw bar.  Extending upward from the base is a depth gauge portion and a cutting portion separated by a recess.  The depth gauge portion precedes the cutting portion in its path through the wood.  The depth gauge, as its name implies, controls the depth of the cut made by the chain.


4
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE


5
A saw chain is identified primarily by its pitch.  The pitch of the chain is the average distance between the centers of three successive rivet holes.  The pitch of a particular link is the distance between the centers of the rivet openings in such a link.2


6
The early saw chains had pitches of 5/8 inch and higher.  The first consumer saws used chains with a pitch of 1/4 inch.  This size chain was an efficient cutting device but, because of the number of links required, it was expensive to manufacture.


7
In 1972, the high cost of the 1/4 inch chain led Omark to begin the development of a less expensive chain for use on consumer chain saws.  Graversen, who worked for Omark, ultimately applied his efforts in developing a 3/8 inch pitch chain which incorporated cutting links used on the 1/4 inch chain.  The cutting link was redesigned with a longer base to maintain chain stability.


8
This chain also utilized what can be termed a guard portion on the drive links that extended upward to protect the depth gauge and lessen the danger of "kickback."  Kickback is the tendency of chain saws to react violently upward if an object contacts the chain as it travels around the upper portion of the nose of the saw bar.  The bar is the portion of the saw on which the chain rotates.  Conventional saw chains typically had depth gauges with substantially straight leading edges.  As the chain travels around the upper portion of the nose of the bar, the leading edge of the depth gauge can become exposed and hook on branches and other objects.  Such hooking could then rapidly and powerfully force the bar of the saw up towards the operator.  Numerous injuries have resulted from this phenomenon.  Prior to the Graversen invention, the universally adopted method of minimizing kickback was the use of safety or guard links.  These links were designed to protect the leading edge of the depth gauge as the cutting links travel around the nose of the bar.  While these safety links helped lessen kickback, they did not prevent it.  They also reduced the efficiency of the saw chain and increased costs.


9
With this in mind, Graversen then redesigned the depth gauge on his extended pitch chain.  He removed the guard portion on the drive link and then reshaped the depth gauge by sloping it rearwardly from the base up to a point rear of the front rivet opening.  Tests showed the chain to cut faster than the standard 1/4 inch chain.  It also exhibited virtually no kickback.  Marketing under the name "91" began in the fall of 1974.


10
Graversen first applied for a patent on the chain in September of 1973.  This application contained six claims.  Believing it to read on prior art, 35 U.S.C. § 102, the examiner rejected the initial application.  Claims 1-5 were dropped, a new one, 7, was added, and Graversen sought reconsideration.  In October, 1974, the examiner again rejected the claims.  A new amendment was sought, but this was rejected for procedural reasons.  The original application was then abandoned and a new application, Serial No. 565,150, was filed.  This new application, containing four claims, was allowed and the patent issued on December 30, 1975.3


11
Claim 1, an independent claim, describes a cutter link with a low profile (low cutter height relative to the length of the base portion), and a pivot point located at the most rearward part of the base portion.  Claim 2 is dependent on claim 1 and describes a rearwardly sloping depth gauge extending from the base portion to a peak behind the center of the front rivet hole.  Claim 3 is dependent on claims 1 and 2 and describes a cutting link with the cutting edge located to the rear of a vertical line bisecting the distance between the front and rear rivet holes.  Claim 4 is independent.  It incorporates features similar to the preceding claims.  It calls for a sloping depth gauge with a peak rearward of the front rivet hole, a cutting link with an extended pitch relative to the pitch of the drive link, and a cutting edge rearward of the line bisecting the two cutting link rivet holes.


12
Appellant quickly recognized the utility of the Omark design.  From the fall of 1974 to February 1978, Homelite and Terry, two Textron subsidiaries, purchased approximately 650,000 feet of the chain.  In 1974, Textron began testing the Omark chain in the hope of developing its own extended pitch economy chain.  Eventually, the accused chain, the Pro-Cut 375, was developed and marketed.4


13
There is no dispute that most of the attributes of the patented device appear on the Pro-Cut 375.  Both have an extended pitch, a low profile, a rearward sloping depth gauge with a peak located behind the center of the front rivet hole, and a cutting edge located behind a point bisecting the rivet holes.  Two differences in dimension exist and these form much of the basis for Textron's appeal.  First, the location of the pivot point is not at the most rearward place on the base of the cutting link as called for in claim 1.  Second, the peak of the depth gauge is not located behind the front rivet hole opening as claim 4 seems to require.


14
Prior to trial, Omark filed a disclaimer of claim 1 in the Patent Office and thereby restricted its claim of infringement at trial to claims 2, 3, and 4.  Apparently, the disclaimer was filed in the belief that claim 1 read on prior art.  Claim 1 remains significant, however, because claims 2 and 3 are dependent on it.

II. DISCUSSION

15
There are two broad issues presented on appeal.  The first involves the validity of the patent.  Textron claims that based on the prior art, the patent is invalid for obviousness.  It also asserts that the patent is invalid because of inadequate specification.  The second issue concerns whether the accused device infringes on the patent.  In this context, Textron argues that its saw chain is not the equivalent of the subject chain.  Furthermore, it asserts that the doctrine of file wrapper estoppel precludes a finding of equivalence.


16
At the outset, Textron claims that the trial judge improperly construed the patented device.  Textron asserts that the judge analyzed the patent in terms of its commercial embodiment rather than on the claims as written.  See Magnavox Co. v. Hart & Reno, 73 F.2d 433, 445-446 (9th Cir. 1934).  Textron fails, however, to point to any place in the record which shows the trial court construed the patent only in terms of the commercial embodiment.  There is also no showing that the production version of the patent, the 91 saw chain, falls outside the claims of the patent.  Textron's contention in this respect does not merit further consideration.

A. Validity
1. The Presumption of Validity

17
All patents are presumed valid.  35 U.S.C. § 282.  This presumption can be overcome only by clear and convincing evidence.  Speed Shore Corp. v. Denda, 605 F.2d 469, 471 (9th Cir. 1979); Santa Fe-Pomeroy, Inc. v. P & Z Co., 569 F.2d 1084, 1091 (9th Cir. 1978).


18
Textron contends that the presumption in favor of the validity of the Graversen patent was lost because of the failure of the patent examiner to consider several relevant prior art references.  The trial court made a detailed factual inquiry into the prior art and found that none of the references cited by Textron were more pertinent than those cited by the Patent Office.  As observed by this court, " '(a)lleged art that is cumulative to cited art does not weaken or destroy the presumption of validity' ....  And the presumption is further strengthened on appeal where, as here, the trial court conducted an independent examination of the pertinent prior art and concluded that the patent was validly issued."  Saf-Gard Products, Inc. v. Service Parts, Inc., 532 F.2d 1266, 1271 (9th Cir.), cert. denied, 429 U.S. 896, 97 S.Ct. 258, 50 L.Ed.2d 179 (1976) (citations omitted).


19
The ultimate issue of patent validity is a question of law.  But, the factual findings necessary to the determination of validity are binding on appeal unless clearly erroneous.  Speed Shore, supra, 605 F.2d at 471.  The trial judge heard substantial evidence on the prior art cited by the Patent Office.  He heard evidence on the prior art references cited by Textron.  He concluded the prior art cited by Textron was not relevant because it did not address itself to the solution of the problem of the invention.  Eibel Process Co. v. Minn. & Ont.  Paper Co., 261 U.S. 45, 67-68, 43 S.Ct. 322, 329-30, 67 L.Ed. 523 (1923); Bianchi v. Barili, 168 F.2d 793, 796 (9th Cir. 1948).  The trial judge's findings are not clearly erroneous.


20
2. Inadequate Specification Under 35 U.S.C. § 112


21
Textron contends claims 2 and 3 are invalid because there are elements of these claims that are not found in the written specification.  35 U.S.C. § 112 states in pertinent part:


22
"The specification 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, or with which it is most nearly connected, to make and use the same, and shall set forth the best mode contemplated by the inventor of carrying out his invention."


23
This court has recognized, however, that the "(a)bsence of a description in the specification is not, by itself, fatal to the patentability of an invention."  Speed Shore, supra, 605 F.2d at 473.  Resort may be made to the drawings to cure omissions in the description.  Id.; see Hensley Equipment Co. v. Esco Corp., 375 F.2d 432, 435 (9th Cir. 1967).  Appellant's own expert testified that one skilled in the art could, by using the drawings and the specification, cure any deficiencies in the written description.  (Testimony of Neumeier, Reporter's Transcript, Volume II, at 345-348).  We find no error in the district court's holding that the patent in suit meets the requirements of 35 U.S.C. § 112.

3. Obviousness

24
Textron's primary argument for invalidating the Graversen patent is 35 U.S.C. § 103.  Section 103 provides that a device is not patentable:


25
"if the differences between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art to which said subject matter pertains."


26
The Supreme Court has held that a determination of obviousness requires a three-part factual inquiry: (1) the scope and the content of the prior art; (2) the differences between the prior art and the claims at issue; and (3) the level of ordinary skill in the art.  Graham v. John Deere Co., 383 U.S. 1, 17, 86 S.Ct. 684, 693, 15 L.Ed.2d 545 (1966).  Secondary considerations such as the commercial success of the patented subject, the failure of others to solve the problem, and long felt, but unresolved, needs in the subject area are also relevant.  Graham, 383 U.S. at 17-18, 86 S.Ct. at 693-94.


27
A related issue is whether, as Textron argues, the Graversen patent is merely a combination of elements previously known in the prior art.  If so, this court will rigidly scrutinize the patent and impose the additional requirement that the combination must have produced unusual or surprising consequences at the time it was made in order to be non-obvious.  M-C Industries v. Precision Dynamics Corp., 634 F.2d 1211, 1214 (9th Cir. 1980); Photo Electronics Corp. v. England, 581 F.2d 772, 775 (9th Cir. 1978).  This requirement "is not inconsistent with, but merely in application of, the general rule stated in § 103...." NDM Corp. v. Hayes Products, Inc., 641 F.2d 1274, 1280 (9th Cir.), cert. denied, --- U.S. ----, 102 S.Ct. 970, 71 L.Ed.2d 109 (1981), quoting Reeves Instrument Corp. v. Beckman Industries Inc., 444 F.2d 263, 271 (9th Cir.), cert. denied, 404 U.S. 951, 92 S.Ct. 283, 30 L.Ed.2d 268 (1971).  The rationale of this more stringent test is that non-obviousness is less likely to occur in combination patents which are simply amalgams of old elements.  NDM, supra, 641 F.2d at 1280.  The factual findings underlying the obviousness determination are reviewed under Rule 52(a)'s clearly erroneous standard.


28
(a) Claims 2 and 3


29
Textron contends that the scope and content of the prior art made the Graversen invention obvious.  In particular, Textron argues that the prior art disclosed the use of a rearwardly sloping depth gauge.  As noted earlier, the trial judge analyzed the prior art in detail.  He found that although some of the individual elements of the combination called for by claims 2 and 3 could be found in the prior art, the combination itself was not obvious.  In this respect, the trial judge correctly recognized that 35 U.S.C. § 103 directs the inquiry of obviousness to focus on the " 'subject matter as a whole' and not (on) the elements of a claimed combination and their individual novelty."  Reeves Instrument, supra, 444 F.2d at 270.  Textron's attempt to limit the inquiry to individual elements of the patented structure is, therefore, improper.  In addition, only two prior art references sought to eliminate kickback by attempting to prevent the depth gauge from engaging an object.  One of these references utilized a separate guard link to prevent the problem.  The other, commonly called the "chicken beak" chain, had a depth gauge that projected forwardly over the end of the preceding link.  It did not prevent kickback and in fact exacerbated the phenomenon.


30
Textron next asserts that any differences between claims 2 and 3 and the prior art are negligible.  In doing so, it points to an example of prior art, the "chamfer chain," which is said to contain the limitations imposed by claims 2 and 3.5  But again, Textron limits its argument to particular elements of the patent and not to the combination as a whole.


31
An analysis of the scope of the prior art and the differences between the prior art and the patent does not end the inquiry.  The key determination is whether, as evinced by the prior art, the level of ordinary skill in the art was such that the combination of elements in the Graversen design was obvious.  This determination is guided by an inquiry into "the problem allegedly solved by the invention and the efforts of others to arrive at a satisfactory solution."  Reeves Instrument, supra, 444 F.2d at 271.  The problem allegedly solved was kickback, a vexing problem with often harmful results.  Testimony established that the Graversen invention substantially reduced, if not totally eliminated, the tendency of a saw to kick back.  Others in the industry had not achieved such results.  Witnesses testified that it was believed that the use of a guard link was the best way to minimize kickback.  Guard links did not, however, reduce kickback to the same extent as Graversen's saw chain.  Also, those devices lowered the saw's efficiency and increased costs.  That the level of skill in the art was not such that Graversen's invention was obvious is best summed up by the statement of Mr. Bailey, a saw chain designer and witness for Omark, who testified "if we thought we could have done it, we would have done it."  (Reporter's Transcript, Volume II at 249.)


32
Secondary considerations strongly support the finding of non-obviousness.  The patent was immediately a commercial success.  Graham, supra, 383 U.S. at 18, 86 S.Ct. at 694.  The extended pitch design of the patent was adopted by a number of other chain manufacturers.  The chain design also helped resolve a long felt need, the elimination of kickback.  Id.


33
At this point, we must return to the question whether the Graversen patent merely entails a combination of old elements.  The trial court held first that the patent achieved unusual results, and second that such a finding was unnecessary because the combination involved a new element.  See, e.g., Austin v. Marco Dental Products, Inc., 560 F.2d 966, 972 (9th Cir. 1977), cert. denied, 435 U.S. 918, 98 S.Ct. 1477, 55 L.Ed.2d 511 (1978).  We agree with the district court's finding that the Graversen invention had unusual and surprising consequences and, therefore, it is unnecessary to determine whether it actually incorporated new elements.  It is sufficient that claims 2 and 3 present a novel combination of interdependent elements which create a less costly device that is also safe and efficient.  This determination is guided by Graham's three-part inquiry and there is no need to recite what was said previously.  The trial judge heard and weighed evidence which tended to establish that the Graversen saw chain reduced kickback to such a level it was virtually nonexistent.  The trial judge accepted that evidence.  His finding is not clearly erroneous.  We have little difficulty, then, in concluding that the reduction or elimination of kickback was a "new" result.  It simply had not occurred before.  Nor is it hard to agree that the result was unusual.  Graversen combined several elements in an effort to produce a lower cost saw chain.  He acquired, in addition, a chain which was also efficient and safe.


34
(b) Claim 4


35
Claim 4, being independent, must be separately analyzed.  It is composed of three primary elements, the foremost calling for a rearward sloping depth gauge.  Importantly, claim 4 is not limited to a low profile cutting link as are claims 2 and 3.  Much of what was said with respect to the obviousness of claims 2 and 3 applies to claim 4.  For the following reasons, we affirm the district court's holding that claim 4 is not invalidated because of obviousness.


36
First, the prior art as analyzed by the trial court did not disclose a cutting link of the same configuration as that in claim 4.  It is true, as Textron asserts, the prior art did include cutting links with depth gauges that slope rearwardly.  However, a comparison of these links shows they curved downward to a substantially vertical leading edge.  The term "sloping" could have been better defined in the claim.  Resort may be had, however, to the drawings in order to interpret a claim.  Del Mar Engineering Laboratories v. Physio- Tronics, Inc., 642 F.2d 1167, 1172 (9th Cir. 1981).  The drawings accompanying the Graversen patent exhibit a depth gauge without a leading edge that is substantially vertical.


37
The level of skill in the art at the time of the Graversen invention taught that safety or guard links were necessary to reduce kickback.  Graversen eliminated those devices from his safety chain.  This was an aberration from industry practice.  Textron argues that it was a simple and obvious step from using a guard link to using a contoured depth gauge such as that adopted by Graversen.  But, a patent will not be invalidated simply because "it embodies a solution which seems simple and obvious with the benefit of hindsight."  Saf-Gard Products, supra, 532 F.2d at 1272; Palmer v. Orthokinetics, Inc., 611 F.2d 316, 323 (9th Cir. 1980).  We cannot say, then, the district court clearly erred in its factual findings supporting the conclusion that the combination of elements in claim 4 was non-obvious.


38
We also conclude the combination of elements in claim 4 produced an unusual and surprising result-the virtual elimination of kickback.  As noted earlier, no other saw chain had been able to solve this problem.  Graversen discovered the utility of his depth gauge design after modifying a standard chain.  It was his hope to reduce costs and maintain efficiency.  By eliminating the guard link, however, he also reduced kickback substantially.  It is important to recognize that Graversen's saw chain was designed for use on consumer chain saws.  Chain saws are inherently dangerous devices.  That dangerous proclivity is exacerbated when the saw is placed in the hands of one with little or no training in its use.  By developing a chain which greatly reduced the danger to consumers while at the same time lowering costs, Graversen created an invention with not only unusual results, but also highly beneficial ones.


39
That this court will closely scrutinize combinations does not mean the patent's presumption of validity is vitiated.  In this respect, Textron has a heavy burden and it must rebut the presumption by clear and convincing evidence.  Speed Shore, supra, 605 F.2d at 471.  Based on the foregoing analysis, we cannot say Textron met its burden.  See Smith International, Inc. v. Hughes Tool Co., 664 F.2d 1373 (9th Cir.), cert. denied, --- U.S. ----, 102 S.Ct. 2242, 72 L.Ed. 851 (1982).

B. Infringement

40
The trial court held Textron's Pro-Cut 375 saw chain infringed on claims 2, 3, and 4.  As we find this holding of the trial court to be supported by the evidence and a proper application of the law, we affirm it as well.


41
The district court's finding of infringement was based on an application of the doctrine of equivalents.  Generally, to determine whether there is an infringement the court must at the outset look to the words of the claim.  Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 607, 70 S.Ct. 854, 855, 94 L.Ed. 1097 (1950).  Even if the accused device does not read literally on the claim, an infringement may still be found under the doctrine of equivalents if the "two devices do the same work in substantially the same way, and accomplish substantially the same result...."  Graver, 339 U.S. at 608, 70 S.Ct. at 856.  In making this determination, "the court must look at the similar device in the context of the patent, the prior art, and the particular circumstances of each case."  Wilden Pump & Eng.  Co. v. Pressed & Welded Products Co., 655 F.2d 984, 987 (9th Cir. 1981).  The court should also consider whether persons reasonably skilled in the art would have known of the interchangeability of the devices.  Graver, supra, 339 U.S. at 609, 70 S.Ct. at 856.  Generally, a finding of infringement is a question of fact and binding on appeal unless clearly erroneous.  See CS&M, Inc. v. Covington Bros. Technologies, 678 F.2d 118 (9th Cir. 1982).  Here, however, there is no dispute as to the construction of the accused and patented devices.  In such a situation, the determination of infringement can be treated as a question of law.  Id.  Nonetheless, our determination of infringement should still be guided by the trial court's underlying findings of fact which are supported in the record.  Our review will entail ascertaining whether the trial court applied the correct rule of law to those facts.


42
At the outset, Textron contends that the district court improperly placed the burden of proof regarding equivalency on it (Textron) rather than on Omark.  The trial court made no express statement with respect to the burden of proof.  We can discern no error, however, where both parties offered evidence from their respective experts regarding the design and function of the saw chains in question.  Clearly, there was sufficient evidence presented by Omark to raise at least an inference that the devices in issue were equivalent.  Textron's contention is, therefore, without merit.


43
Textron does not dispute that at least one part of the equivalents test has been met.  It readily concedes that the accused saw chain achieves the same results as the patented device-increased efficiency and a minimization of the danger of kickback.  It argues, however, that its chain does not use the same means in the same way as the patented chain in order to achieve the like results.  Mobil Oil Corp. v. Filtrol Corp., 501 F.2d 282, 292 (9th Cir. 1974).


44
Textron stipulated at trial that the only issue with respect to the infringement of claims 2 and 3 involved the location of the pivot point on the cutting link.  Textron argues that because the pivot point on the accused saw chain is not located at the rearward most part of the cutting link base, the same design or "means" is not used to accomplish the like result.6  This argument improperly focuses on the elements of the patent claims in isolation rather than as an interdependent whole.  Also, the testimony established and the trial court found the design of the rearward section of the Pro-Cut 375, including its pivot point location, served no functional purpose.  The effect of that finding is the pivot point is in substantially the same functional location in both saw chains.  The trial court did not err in holding that the Pro-Cut 375 design was the equivalent of claims 2 and 3.


45
Textron also stipulated at trial that the only infringement issue with respect to claim 4 was the location of the peak of the depth gauge.  Claim 4 teaches, among other things, that the peak of the depth gauge be rearward of the front rivet opening of the cutting link.  The accused chain has a depth gauge peak located to the rear of the center of the rivet hole, but not behind the rivet hole itself.  The trial court held the accused chain was the equivalent of the patented device.  We can discern no error.  The trial judge could properly find that among the several interdependent elements of claim 4, and in particular the requirement that the depth gauge be rearwardly sloping, the exact location of the peak of the depth gauge was not of primary importance.  See International Manufacturing Co. v. Landon, Inc., 336 F.2d 723, 727-728 (9th Cir. 1964), cert. denied, 379 U.S. 988, 85 S.Ct. 701, 13 L.Ed.2d 610 (1965).


46
Textron also contends the accused chain is not the equivalent of the subject chain because a different attribute, that of a lower depth gauge setting than used in the patented device, results in the elimination of kickback.  In this respect, Textron asserts that it is not the attributes claimed in the patent and found on its device, such as an extended pitch, a sloping depth gauge, a low profile, a rearward pivot point, etc., which minimize kickback.  In fact, the evidence presented supports the conclusion that a lower depth gauge setting can reduce kickback.  The patented device, however, uses a higher setting and still exhibits the same minimum tendency to kickback.  The trial court could properly hold, then, that a lower depth gauge setting is insufficient to differentiate the accused saw chain.  Instead, it is the similar features which lead to the similar results of greater efficiency and less kickback.7


47
The final issue concerning infringement is whether, as Textron contends, the doctrine of file wrapper estoppel precludes a finding that the accused chain reads on claims 2 and 3 of the subject chain.  Under this rule of construction, an applicant who has surrendered, amended, narrowed, or otherwise limited his claims in order to secure the allowance of a patent may not later recapture through the doctrine of equivalents what he has given up.  Graham, supra, 383 U.S. at 33, 86 S.Ct. at 701-02; International Manufacturing Co., supra, 336 F.2d at 727.


48
As noted, Textron stipulated at trial that the only issue with respect to the infringement of claims 2 and 3 was whether the accused chain has a pivot point located at the rearward most point of the base portion of the cutting link.  The issue can be narrowed, then, to whether file wrapper estoppel precludes a finding of equivalence because of the different dimensional location of the pivot point in the Pro-Cut 375.


49
The original claims of the application were rejected because the combination presented was, as a whole, unpatentable over the references cited.  The district court found the requirement that the pivot point be located at the most rearward part of the base of the cutter was unnecessary to distinguish the claim over the prior art cited in rejection of the earlier claims.  Thus, Omark is not recapturing something it had given up to secure issuance of the patent.  International Manufacturing Co., supra, 336 F.2d at 727.  Nor should the patent be strictly limited to cover only those structures having a pivot point located at the most rearward point in the base.  "(A)n applicant should not be presumed to have made a disclaimer broader than necessary to yield to the actual challenge of the claim."  Ziegler v. Phillips Petroleum Co., 483 F.2d 858, 871 (5th Cir.), cert. denied, 414 U.S. 1079, 94 S.Ct. 597, 38 L.Ed.2d 485 (1973); see Nationwide Chemical Corp. v. Wright, 584 F.2d 714, 719-720 (5th Cir. 1978).  Furthermore, the amendment to the original claims contained a combination of elements.  The exact location of the pivot point was not the "heart" of the invention but only part of that combination.  We cannot say, therefore, that finding file wrapper estoppel inapplicable was either clearly erroneous or a misapplication of the law.  International Manufacturing Co., supra, 336 F.2d at 727-728.

III. CONCLUSION

50
The judgment of the district court holding U.S. Patent No. 3,929,049 valid and infringed is


51
AFFIRMED.

APPENDIX A

52
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE


53
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE


54
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE

TABLE

55
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE

TABLE

56
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE

APPENDIX B

57
NOTE: OPINION CONTAINS TABLE OR OTHER DATA THAT IS NOT VIEWABLE



*
 The Honorable Walter E. Craig, Senior United States District Judge, District of Arizona, sitting by designation


*
 2 See Footnote 1.  The pitch of this chain would be the average distance between the center of the two rivet holes on the cutting link (C) and the first rivet hole of the tie strap (B)


3
 See Appendix A for a reproduction of the Graversen patent


4
 See Appendix B for a reproduction of the accused saw chain


5
 The chamfer chain (Atkins 1/2 Inch Pitch Cutter), while having a rearwardly inclined depth gauge, also has a substantially vertical leading edge on its depth gauge.  It would not alleviate a saw's tendency to kick back.  The chamfer chain's other attributes do not fall within the essential patent elements


6
 The cutting link on the Pro-Cut 375 has a bulge at the rearward part of the base.  This attribute places the pivot point slightly forward of the most rearward portion of the base as called for in claim 1.  As noted earlier, claims 2 and 3 are dependent on claim 1 and all three must be read as a whole


7
 Hille, a witness for Omark, testified that a lower depth gauge setting can reduce kickback.  He stated further, however, he would expect the lower setting in the Pro-Cut chain to result in only "slightly less kickback."  (Reporter's Transcript, Volume III at 205.)  In addition, Textron stipulated that the locations of the pivot point and the peak of the depth gauge were the only issues with respect to infringement of the patent.  The height of the depth gauge was not in issue


