Clarification of the Proper Use of Extrinsic Evidence in Claim Interpretation: Vitronics Revisited

In the recent case of Pitney Bowes, Inc. v. Hewlett-Packard Co., 51 U.S.P.Q.2d 1161 (Fed. Cir. 1999), the Court of Appeals for the Federal Circuit clarified when courts may properly consult extrinsic evidence when interpreting patent claim language. In so doing, the Court dispelled some common misconceptions about its prior holding in Vitronics Corp. v. Concerptronic, Inc., 90 F.3d 1576 (Fed. Cir. 1996). The Federal Circuit held in Pitney Bowes that it is appropriate for a court to consider extrinsic evidence when interpreting claim terms as long as the court does not rely on the extrinsic evidence to the exclusion of, or in contradiction to, the intrinsic evidence. The Court dispelled a common misconception that Vitronics prohibits consideration of extrinsic evidence except where the meaning of claim terms cannot be conclusively determined from the intrinsic evidence. On the contrary, the Court explains, extrinsic evidence may be consulted even when the meaning of claim terms is clear. The case began as a patent infringement action against Hewlett-Packard and involved an apparatus and method used to vary the size of toner dots in laser printers. Varying the size of toner dots was found to reduce the jagged or uneven appearance of certain characters. Hewlett-Packard moved for summary judgment of non-infringement. A key issue in the summary judgment proceedings was the proper interpretation of the claim term "spots." In granting summary judgment to Hewlett-Packard, the district court used language which indicated that, in interpreting the term "spots," it had taken into consideration an expert affidavit submitted by Hewlett-Packard with its reply brief. On appeal, Pitney Bowes argued that the court erroneously relied on this extrinsic evidence to contradict a claim interpretation that was clear from the intrinsic evidence. The Federal Circuit held that, while extrinsic evidence should not be relied upon to contradict the meaning of claims discernible from careful consideration of the intrinsic evidence, it is still proper for a court to examine extrinsic evidence to confirm or rebut what the intrinsic evidence has established. The Federal Circuit corrected the district court's erroneous assertion that, under Vitronics, if claim terms can be understood by examining only the intrinsic evidence, then consideration of extrinsic evidence is improper. In fact, the Court stated, "it is entirely appropriate, perhaps even preferable, for a court to consult trustworthy extrinsic evidence to ensure that the claim construction it is tending to from the patent file is not inconsistent with clearly expressed, plainly apposite, and widely held understandings in the pertinent technical field." The court went on to state that it is a judge's job to interpret claim language "from the vantage point of one skilled in the art." Thus, expert testimony and other extrinsic evidence which educates the judge about the relevant technology may be a useful tool to judges charged with interpreting technical language.