BISSELL, Circuit Judge, filed an opinion, in which MARKEY, Chief Judge, FRIEDMAN, RICH, DAVIS, NIES and ARCHER, Circuit Judges, joined; BENNETT, Senior Circuit Judge, filed a dissent-in-part, in which COWEN, Senior Circuit Judge, SMITH and NEWMAN, Circuit Judges, joined. NIES, Circuit Judge, filed additional views; NEWMAN, Circuit Judge, filed a commentary.
BISSELL, Circuit Judge.This appeal and cross-appeal are from a judgment of the United States District Court for the Northern District of Georgia, 225 USPQ 558 (N.D.Ga.1984). The district court found that Durand-Wayland’s accused devices do not infringe any claim, literally or under the doctrine of equivalents. Unable to view that finding as clearly erroneous under Fed.R.Civ.P. 52(a), we affirm the judgment of noninfringement and vacate, as moot, that part of the judgment concerning the validity of Pennwalt’s patent.
BACKGROUND
Pennwalt sued Durand-Wayland for infringing claims 1, 2, 10 and 18 (claims-at-issue) of its U.S. Patent No. 4,106,628 (the ’628 patent) on an invention of Aaron J. Warkentin and George A. Mills, entitled “Sorter for Fruit and the Like.” Following a nonjury trial on the issues of patent infringement and validity, the district court, on March 22, 1984, issued an opinion concluding that (1) the claims-at-issue were *933not anticipated by the prior art, (2) the 628 patent had not run afoul of the “on sale” bar of 35 U.S.C. § 102(b) (1982), and (3) the accused devices did not infringe any of the claims-at-issue, either literally or under the doctrine of equivalents. In an unpublished supplemental order of April 26, 1984, the district court concluded as a matter of law that the claims-at-issue would not have been obvious in light of the prior art.
Pennwalt appeals from the district court’s holding of noninfringement, both literally and under the doctrine of equivalents, and its award of costs against Penn-walt. Durand-Wayland appeals from the district court’s validity holdings and its denial of Durand-Wayland’s request for recovery of its attorney fees.
ISSUE
Our disposition of this appeal requires resolution of the single question of whether the district court’s finding of no infringement was clearly erroneous.
OPINION
The ’628 patent claims a sorter. The principal object of the invention is to provide a rapid means for sorting items, such as fruit, by color, weight, or a combination of these two characteristics. The sorter recited in claims 1 and 2 conveys items along a track having an electronic-weighing device that produces an electrical signal proportional to the weight of the item, along with signal comparison means, clock means, position indicating means, and discharge means, each of which performs specified functions. The specification describes the details of a “hard-wired” network consisting of discrete electrical components which perform each step of the claims, e.g., by comparing the signals from the weighing device to reference signals and sending an appropriate signal at the proper time to discharge the item into the container corresponding to its weight. The combined sorter of claims 10 and 18 is a multifunctional apparatus whereby the item is conveyed across the weighing device and also carried past an optical scanner that produces an electrical signal proportional to the color of the item. The signals from the weighing device and color sensor are combined and an appropriate signal is sent at the proper time to discharge the item into the container corresponding to its color and weight.
Durand-Wayland manufactures and sells two different types of sorting machines. The first accused device, the “Microsizer,” sorts by weight only and employs software labeled either Version 2 or Version 5. The second accused device employs software labeled Version 6 and sorts by both color and weight through the use of the “Micro-sizer” in conjunction with a color detection apparatus called a “Microsorter.”
A more complete description of the claimed invention and of the accused devices is set forth in the district court’s opinion. Pennwalt, 225 USPQ at 559-60. The claims-at-issue are set forth in the district court’s opinion. Id. at 564-65.
I.
Literal Infringement
Pennwalt asserts on appeal that all limitations set forth in claims 1 and 2 and some limitations set forth in claims 10 and 18 can be read literally on the accused devices. Pennwalt contends that the district court erred in interpreting the claims by going beyond the means-plus-function language of a claim limitation and comparing the structure in the accused devices with the structure disclosed in the specification. Such comparison allegedly resulted in the court’s reading nonexistent structural limitations into the claims. Pennwalt relies on the statement in Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605, 607, 70 S.Ct. 854, 855, 94 L.Ed. 1097 (1950): “If accused matter falls clearly within the claim, infringement is made out and that is the end of it.” In view of the literal breadth of means-plus-function language in the claims, that “test” for literal infringement would encompass any means that performed the function of a claim element. 35 U.S.C. § 112 (1982). This is not the “test.” The Graver Tank statement predated the inclusion in the 1952 Act of the *934provision specifically permitting “means” limitations, section 112, paragraph 6. See P. Federico, Commentary on the New Patent Law, 35 USCA 1, 25 (1954). As Judge Rich, one of the drafters of the statute, stated in a 1952 address explaining the import of section 112, paragraph 6:
If you adopt this practice, that element or step is to be construed — shall be construed (it is mandatory) — to cover the corresponding structure, material or acts described in the specification and equivalents thereof.
Address before the New York Patent Law Association (November 6, 1952), reprinted in R. Calvert, The Encyclopedia of Patent Practice and Invention Management 17, “Section 112 — Means Claims” (1964).
Thus, section 112, paragraph 6, rules out the possibility that any and every means which performs the function specified in the claim literally satisfies that limitation. While encompassing equivalents of those disclosed in the specification, the provision, nevertheless, acts as a restriction on the literal satisfaction of a claim limitation. Data Line Corp. v. Micro Technologies, Inc., 813 F.2d 1196, 1201, 1 USPQ2d 2052, 2055 (Fed.Cir.1987). If the required function is not performed exactly in the accused device, it must be borne in mind that section 112, paragraph 6, equivalency is not involved. Section 112, paragraph 6, plays no role in determining whether an equivalent function is performed by the accused device under the doctrine of equivalents.
Thus, it was not legal error (as Pennwalt asserts) for the district court to have made a comparison between Durand-Wayland’s structure and the structure disclosed in the specification for performing a particular function. The statute means exactly what it says: To determine whether a claim limitation is met literally, where expressed as a means for performing a stated function, the court must compare the accused structure with the disclosed structure, and must find equivalent structure as well as identity of claimed function for that structure. Palumbo v. Don-Joy Co., 762 F.2d 969, 975, 226 USPQ 5, 8 (Fed.Cir.1985); D.M.I., Inc. v. Deere & Co., 755 F.2d 1570, 1575, 225 USPQ 236, 239 (Fed.Cir. 1985); Radio Steel & Mfg. Co. v. MTD Prods., Inc., 731 F.2d 840, 848, 221 USPQ 657, 663 (Fed.Cir.1984).
Where the issue is raised, it is part of the ultimate burden of proof of the patent owner to establish, with respect to a claim limitation in means-plus-function form, that the structure in the accused device which performs that function is the same as or an equivalent of the structure disclosed in the specification. In essence, Pennwalt erroneously argues that, if an accused structure performs the function required by the claim, it is per se structurally equivalent. That view entirely eliminates the section 112, paragraph 6, restriction and has been rejected in the above-cited precedent of this court.
We need not, and do not, determine whether the district court correctly found no equivalency in structure because the district court also found that the accused devices, in any event, did not perform the same functions specified in the claim. For example, the district court found that the accused devices had no position indicating means which tracked the location of the item being sorted. That finding negates the possibility of finding literal infringement.
II.
Infringement under the Doctrine of Equivalents
Under the doctrine of equivalents, infringement may be found (but not necessarily 1) if an accused device performs substantially the same overall function or work, in substantially the same way, to obtain substantially the same overall result as the claimed invention. Perkin-Elmer Corp. v. Computervision Corp., 732 F.2d *935888, 901-02, 221 USPQ 669, 679 (Fed.Cir.), cert. denied, 469 U.S. 857, 105 S.Ct. 187, 83 L.Ed.2d 120 (1984); Graver Tank, 339 U.S. at 608, 70 S.Ct. at 856. That formulation, however, does not mean one can ignore claim limitations. As this court recently stated in Perkin-Elmer Corp. v. Westinghouse Elec. Corp., 822 F.2d 1528, 3 USPQ2d 1321 (Fed.Cir.1987):
One must start with the claim, and though a “non-pioneer” invention may be entitled to some range of equivalents, a court may not, under the guise of applying the doctrine of equivalents, erase a plethora of meaningful structural and functional limitations of the claim on which the public is entitled to rely in avoiding infringement.... Though the doctrine of equivalents is designed to do equity, and to relieve an inventor from a semantic strait jacket when equity requires, it is not designed to permit wholesale redrafting of a claim to cover nonequivalent devices, i.e., to permit a claim expansion that would encompass more than an insubstantial change. (Citations omitted.)
... [I]n applying the doctrine of equivalents, each limitation must be viewed in the context of the entire claim.... “It is ... well settled that each element of a claim is material and essential, and that in order for a court to find infringement, the plaintiff must show the presence of every element or its substantial equivalent in the accused device.” Lemelson v. United States, 752 F.2d 1538, 1551, 224 USPQ 526, 533 (Fed.Cir.1985) (footnote omitted). To be a “substantial equivalent,” the element substituted in the accused device for the element set forth in the claim must not be such as would substantially change the way in which the function of the claimed invention is performed.
Id. at 1532-33, 3 USPQ2d at 1324-25.
Pennwalt argues that the “accused machines simply do in a computer what the patent illustrates doing with hard-wired circuitry,” and asserts that “this alone is insufficient to escape infringement,” citing Decca Ltd. v. United States, 544 F.2d 1070, 1080-81, 210 Ct.Cl. 546, 563-64, 191 USPQ 439, 447 (1976). If Pennwalt was correct that the accused devices differ only in substituting a computer for hard-wired circuitry, it might have a stronger position for arguing that the accused devices infringe the claims. The claim limitations, however, require the performance of certain specified functions. Theoretically, a microprocessor could be programmed to perform those functions. However, the district court found that the microprocessor in the accused devices was not so programmed.
After a full trial, the district court made findings that certain functions of the claimed inventions were “missing” from the accused devices and those which were performed were “substantially different.” Pennwalt, 225 USPQ at 572. The district court observed that “because the ‘Microsizer’ uses different elements and different operations (on the elements it does use) than the elements and operations disclosed in the patent-in-suit to achieve the desired results, infringement can only be found if the different elements and operations are the legal equivalents of those disclosed in the patent-in-suit.” Id. It is clear from this that the district court correctly relied on an element-by-element comparison to conclude that there was no infringement under the doctrine of equivalents, because the accused devices did not perform substantially the same functions as the Penn-walt invention. For example, the district court found in part:
The machine described in the patent-in-suit uses shift registers that respond to “clock pulses” in order to indicate the various positions of the items to be sorted before each item is discharged. The “Microsizer” does not have any “indicating means” to determine positions of the items to be sorted since the microprocessor stores weight and color data, not the positions of the items to be sorted. After a piece of fruit has been analyzed by the “Microsorter” and while it is in transit from the optical detection means to the weight scale, the color value determined by the “Microsorter” is sorted in a color value queue. A color value queue pointer (which changes in value) points to *936the location of the data corresponding to the next piece of fruit to reach the weight scale. A weight value queue pointer (which also changes in value) is used to correspond to the number of cups between the weight scale and the drop location. The microprocessor software utilizes a random access memory that stores the digital numbers which resulted from the conversion of the analog signals generated by the “Microsorter” and the weight scale, and the queue pointers (under clock control) point to the memory location that has the data about a piece of fruit. The data is never “shifted” around, but rather is just stored in memory until the software routines call for data to be utilized in subsequent portions of the program(s). Thus, the “Microsizer” has neither a “first position indicating means” nor a “second position indicating means.” The machine described in the patent-in-suit produces signals that indicate where the fruit is, i.e. track the progression of each cup. The “Microsizer” does not.
Id. at 569.
Pennwalt argues that the district court erred as a matter of law in interpreting the claims which led to these findings. Penn-walt asserts that the district court looked to the specification and compared the accused devices with the preferred embodiment. As indicated, under the section 112, paragraph 6, analysis, such comparison was entirely correct, but it is readily apparent that the court did not so limit its infringement analysis. The court also looked for equivalent functions.
It is not the province of this court to determine de novo what is the preponderance of the evidence underlying the ultimate finding of no infringement or the subsidiary facts supporting that finding. Indeed, Fed.R.Civ.P. 52(a) prohibits our undertaking the role of the fact finder, which is the domain of the trial court. Anderson v. City of Bessemer City, North Carolina, 470 U.S. 564, 573-74, 105 S.Ct. 1504, 1511-12, 84 L.Ed.2d 518 (1985); Graver Tank, 339 U.S. at 611, 70 S.Ct. at 857. As stated in United States v. United States Gypsum Co., 333 U.S. 364, 395, 68 S.Ct. 525, 541, 92 L.Ed. 746 (1948): “A finding is ‘clearly erroneous’ when, although there is evidence to support it, the reviewing court on the entire evidence is left with the definite and firm conviction that a mistake has been committed.”
Here, if the district court was not clearly erroneous in finding that even a single function required by a claim or an equivalent function is not performed by the Du-rand-Wayland sorters, the court’s finding of no infringement must be upheld. Perkin-Elmer v. Westinghouse, 822 F.2d at 1531, 3 USPQ2d at 1323.
Pennwalt asks us to reweigh the testimony, urging that the testimony of the court-appointed expert, Dr. Vacroux, is so strongly supportive of the contrary finding of infringement under the doctrine of equivalents that the district court’s finding of no infringement cannot stand. Penn-walt, however, misconstrues the effect of Dr. Vacroux’s testimony. Dr. Vacroux was a technical, not a legal, expert. He was not expected to, and did not, analyze infringement under a legal standard. He was not concerned, for example, with the scope of equivalents to which the claims were entitled in view of the prosecution history. In this light, the reports and testimony of Dr. Vacroux fully support the district court’s finding of no infringement, rather than Pennwalt’s position.
Pennwalt relies on the conclusory statement in Dr. Vacroux’s initial written report in which he characterized the accused devices as “functionally equivalent” to the “invention.” However, Dr. Vacroux also stated therein that “the new designs could be totally equivalent to those they replaced, although the components and methods used differed significantly.” (Emphasis added.) Further, when Dr. Vacroux was called to testify, and, in response to detailed questioning by the court, Dr. Va-croux testified that the accused devices performed “some" of the same type of operations but “in a different way” from the claimed invention. Specifically, Dr. Va-croux answered a question by the court as follows:
*937Dr. Vacroux: They [the accused and claimed devices] are not equivalent, but functionally the internal operations I would say internally are functionally equivalent because they perform some of the same type of operations. They compare, they shift, they add so we do have the same type of functions internally but done in a different way. [Emphasis added.]
Dr. Yacroux’s statement that the accused devices performed only “some of the same type of operations” supports the court’s finding that some were not. It does not conflict with any of his other testimony or with his written report. Thus, on the issue of whether the accused devices performed each of the functional limitations of the claim or its equivalent and, thus, operated in substantially the same way, the district court followed its expert precisely. The court cannot be faulted for finding no infringement where the expert’s testimony as to facts negates a finding of equivalency under the correct legal standard. See Perkin-Elmer v. Westinghouse, 822 F.2d at 1531-32, 3 USPQ2d at 1323-24.
With respect to the scope of equivalent functions, the court correctly limited the claims, based upon review of the prosecution history, stating that “the claims of the patent should be read in light of the careful phraseology [of functions] chosen by the inventors” because “the machine disclosed in the patent-in-suit was carefully described so that it did not read on the prior art.” Pennwalt, 225 USPQ at 570. As the court correctly noted, the invention was not a pioneer, but an improvement in a crowded art. The claims are “broad” with respect to what type of product can be sorted, i.e., “items” and, thus, sorters of all types of “items” fall within the relevant prior art. The claims are narrow, however, with respect to how the claimed sorter operates. Originally, the claims contained no position indicating means element with its associated functional limitations. The addition of that element was crucial to patentability. A device that does not satisfy this limitation at least equivalently does not function in • substantially the same way as the claimed invention. Perkin-Elmer v. Westinghouse, 822 F.2d at 1532, 3 USPQ2d at 1324; Chemical Eng’g Corp. v. Essef Indus., Inc., 795 F.2d 1565, 1572-73, 230 USPQ 385, 390-91 (Fed.Cir.1986).
The trial court found that the accused devices do not have any position indicating means to determine positions of the items to be sorted. Specifically with respect to claims 10 and 18, the court correctly held that “the microprocessor stores weight and color data, not the positions of the items to be sorted.” Pennwalt, 225 USPQ at 569. Since each of the claims-at-issue requires a position indicating means and the same analysis applies to each, we set forth only the relevant language of claim 10:
first position indicating means responsive to a signal from said clock means and said signal from said second comparison means for continuously indicating the position of an item to be sorted while the item is in transit between said optical detection means and said electronic weighing means,
second position indicating means responsive to the signal from said clock means, the signal from said first comparison means and said first position indicating means for generating a signal continuously indicative of the position of an item to be sorted after said item has been weighed.
The testimony of Dr. Alford, Durand-Wayland’s expert, was that the accused machine had no component which satisfied either of the above limitations defining position indicating means, and Pennwalt has admitted that the accused machines do not sort by keeping track of the physical location of an item in transit, continuously or otherwise, as required by each of these limitations.
Pennwalt argues that there is a way to find out where an item is physically located on the track in the accused machine. Its witness, Dr. Moore, testified “you could find the location of a particular fruit as it moves from the scale to the drop by counting the distance from the stored value for that fruit back to the place the pointer is indicating at the start of the queue.” (Em*938phasis added.) Dr. Alford, Durand-Way-land’s expert, admitted this was possible. Thus, Pennwalt asserts that the accused devices have “position indicating means.”
One need not explain the technology to understand the inadequacy of Dr. Moore’s testimony. As Dr. Moore himself indicates, the accused machine simply does not do what he explains “could” be done. It is admitted that the physical tracking of fruit is not part of the way in which the Durand-Wayland sorter works, in contrast to the claimed sorter which requires some means for “continuously indicating the position of an item to be sorted.” While a microprocessor theoretically could be programmed to perform that function, the evidence led the court to a finding that the Durand-Wayland machines performed a substantially different function from that which each of the claims requires.
With respect to the other limitations of claim 10, Pennwalt admits that the asserted “position indicating means” of Durand-Wayland does not meet the limitation that the means must be “responsive to ... said signal from said second comparison means” because no comparison is made on the Du-rand-Wayland machine before the discharge point. However, Pennwalt contends that Durand-Wayland “has merely changed the position of an operable element, but the operation and results achieved are the same as those claimed.” Pennwalt’s analysis is flawed in significant respects.
First, the claim requires that the “position indicating means” must be responsive to certain specified signals. Thus, finding some combination of components in the accused device that might also be labeled a “position indicating means” is a meaningless exercise when such combination is not responsive to the specified signal. See Polaroid Corp. v. Eastman Kodak Co., 789 F.2d 1556, 1570, 229 USPQ 561, 572 (Fed.Cir.1986) (argument “based on truncation of the claim language” rejected). As stab ed in Panduit Corp. v. Dennison Mfg. Co., 810 F.2d 1561, 1576, 1 USPQ2d 1593, 1603, (Fed.Cir.), cert. denied, — U.S. —, 107 S.Ct. 2187, 95 L.Ed.2d 843 (1987):
In interpreting the claims, the district court committed fundamental legal error when it analyzed each by a single word description of one part of the claimed tie. In patent law, a word (“teeth”; “hinge”; “ledge”) means nothing outside the claim and the description in the specification. A disregard of claim limitations, as here, would render claim examination in the PTO meaningless. If, without basis in the record, courts may so rewrite claims, the entire statutory-regulatory structure that governs the drafting, submission, examination, allowance, and enforceability of claims would crumble.
Second, the district court correctly rejected Pennwalt’s assertion that the memory component of the Durand-Wayland sorter which stores information as to weight and color of an item performed substantially the same functions as claimed for the position indicating means. The district court found that a memory function is not the same or substantially the same as the function of “continuously indicating” where an item is physically located in a sorter. On this point the record is indisputable that before the words “continuously indicating” were added as an additional limitation, the claim was unpatentable in view of prior art which, like the accused machines, stores the information with respect to sorting criteria in memories, but did not “continuously” track the location. See, e.g., U.S. Patent No. 3,289,832 issued to Ramsey.
Thus, the facts here do not involve later-developed computer technology which should be deemed within the scope of the claims to avoid the pirating of an invention. On the contrary, the inventors could not obtain a patent with claims in which the functions were described more broadly. Having secured claims only by including very specific functional limitations, Penn-walt now seeks to avoid those very limitations under the doctrine of equivalents. This it cannot do. Graham v. John Deere Co., 383 U.S. 1, 33-34, 86 S.Ct. 684, 701-02, 15 L.Ed.2d 545 (1965); Chemical Eng’g Corp., 795 F.2d at 1572 n. 8, 230 USPQ at 391 n. 8; see also Exhibit Supply Co. v. *939Ace Patents Corp., 315 U.S. 126, 136, 62 S.Ct. 513, 518, 86 L.Ed. 736 (1942); Coleco Indus., Inc. v. United States Int’l Trade Comm’n, 573 F.2d 1247, 1257-58, 65 C.C.P.A. 105, 116-17, 197 USPQ 472, 479-80 (1978). Simply put, the memory components of the Durand-Wayland sorter were not programmed to perform the same or an equivalent function of physically tracking the items to be sorted from the scanner to the scale or from the scale to its appropriate discharge point as required by the claims.2
Contrary to Pennwalt’s arguments, the district court did not disregard the need to consider a range of equivalent functions under the doctrine of equivalents. Rather, upon evaluation of the evidence, the court concluded, as a fact, that no component in the Durand-Wayland devices performed a function within the permissible range of equivalents for the function of the first position indicating means. That function is required by all of the claims-at-issue. No means in the accused devices performs that function and thus there could be no literal infringement. No means with an equivalent function was substituted in the accused devices and thus there can be no infringement under the doctrine of equivalents. The district court’s finding of no infringement is not clearly erroneous.
Attorney Fees
Durand-Wayland has not shown that the district court’s refusal to find the case exceptional and award it attorney fees was based on clearly erroneous findings. Reactive Metals & Alloys Corp. v. ESM, Inc., 769 F.2d 1578, 1582-83, 226 USPQ 821, 824 (Fed.Cir.1985).
CONCLUSION
We affirm the judgment based on the finding of no infringement, the award of costs, and the denial of attorney fees to Durand-Wayland. There being no indication that Durand-Wayland’s cross-appeal on validity extends beyond the litigated claims or the accused devices found to be noninfringing, we dismiss the cross-appeal as moot and vacate that part of the judgment concerning the validity of Pennwalt’s patent.
AFFIRMED-IN-PART AND VACATED-IN-PART.
. The doctrine of equivalents is limited in that the doctrine will not extend (1) to cover an accused device in the prior art, and (2) to allow the patentee to recapture through equivalence certain coverage given up during prosecution. Loctite Corp. v. Ultraseal Ltd., 781 F.2d 861, 870, 228 USPQ 90, 96 (Fed.Cir.1985).
. That a patent applicant narrows his claim to secure a patent does not always mean that prosecution history estoppel completely prohibits the patentee from recapturing some of what was originally claimed. The amount of coverage retained depends on the circumstances of each case. See, e.g., Loctite Corp. v. Ultraseal Ltd., 781 F.2d 861, 870, 228 USPQ 90, 96 (Fed.Cir.1985); Bayer Aktienegesellschaft v. Duphar Int'l Research, 738 F.2d 1237, 1243, 222 USPQ 649, 653 (Fed.Cir.1984); Hughes Aircraft Co. v. United States, 717 F.2d 1351, 1362, 219 USPQ 473, 481 (Fed.Cir.1983).