When a claim is construed, claim terms should generally be given their “ordinary and customary meaning.” Phillips v. AWH Corp., 415 F.3d 1303, 1312-14 (Fed. Cir. 2005). The meaning of a claim is determined by using intrinsic evidence, which includes the claims, the specification, and the prosecution history and by using extrinsic evidence, which includes dictionaries. Id. at 1319. However, extrinsic evidence in determining the meaning of a claim may be less reliable than intrinsic evidence: “extrinsic evidence may be useful to the court, but it is unlikely to result in a reliable interpretation of patent claim scope unless considered in the context of intrinsic evidence.” Id. This court has cautioned that “heavy reliance on the dictionary divorced from the intrinsic evidence risks transforming the meaning of the claim term to the artisan into the meaning of the term in the abstract, out of its particular context, which is the specification.”

The CAFC admonished the district court for relying on dictionary definitions rather than following the Phillips v. AWH decision of preferring intrinsic evidence over extrinsic.

In the present case, the proper claim construction based on the teachings in Phillips begins with the claim language. First, the claim language itself limits and describes “surface” by including the language “generally planar.” Mr. Byrne argues that a “generally planar surface” exists on the accused device because “a plurality of points on the surface of the wire edge guide lie in a plane.” However, as Black & Decker points out, the claims do not cover a “surface that has two or more points in a plane,” but recite only a “generally planar surface.” Further, the ’815 patent teaches that the purpose of the “generally planar surface” is as a flail stabilizer, and this flail stabilizing purpose is achieved when the surface itself is “generally planar.” Thus, based on the language of the claims, the “surface” claimed in the ’815 patent must be “generally planar” itself and not merely have points lying in a plane.

Second, the specification of the ‘815 patent further supports the claim language that the surface itself is “generally planar.”

Finally, the prosecution history described... a two-dimensional surface that is not narrow but has a width less than the feed increment of the trimmer head and is itself generally planar.

The district court erred in construing “surface” because it gave too much preliminary weight to dictionary definitions without relying on intrinsic evidence, as cautioned against in Phillips. The court should have applied the teachings of Phillips and should have considered the claims, the specification, the prosecution history, and if necessary the dictionary when it construed the claims.

The appeals court distinguished, in construing claims in light of the accused product, between what should be construed (correct) and how it terms should be construed (incorrect).

Mr. Byrne complains that the district court erred by considering the accused device when construing the claims. However, there is a distinction between performing claim construction and deciding what should be construed. A court may consider the accused device to determine what part of the claim must be construed. Exigent Tech. v. Atrana Solutions, Inc., 442 F.3d 1301, 1309 n.10 (Fed. Cir. 2006). But, the court cannot construe claims based on the accused device. Id. The district court in this case did not err when it considered the accused device to determine that it should construe the claim term “generally planar surface.”

Byrne had waived doctrine of equivalents by not arguing it in his opening brief. In view of its own claim construction, the CAFC also found literal "noninfringement because Black & Decker’s device does not have the “generally planar surface” claimed by the ‘815 patent."

Despite the district court’s erroneous approach in construing the claims of the ’815 patent, Black & Decker is nonetheless entitled to summary judgment of noninfringement because its devices do not include a “generally planar surface.” We therefore affirm the judgment of the district court.