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Dictionary finishes third in patent claim construction

Cantor Colburn June / July 2023 IP Newsletter

Cantor Colburn June / July 2023 IP Newsletter

Dictionaries have their place, but when it comes to interpreting the meaning of patent terms, that place generally isn’t first. In Grace Instrument Indus., LLC v. Chandler Instruments Co., LLC, the U.S. Court of Appeals for the Federal Circuit laid out just when the dictionary may play a role in such “claim construction.”

District court blows a hole in patent

The patent at issue was for a liquid pressurized viscometer used to measure drilling fluid viscosity when drilling oil wells. The viscometer is designed to eliminate measuring errors found in other methods through the use of an “enlarged chamber.”

Grace Instrument Industries, the patent holder, sued Chandler Instruments for infringement. The district court ruled for Chandler, finding that the term “enlarged chamber” was indefinite, rendering the patent invalid. Because the term was a “term of degree,” the court said, it must be compared against something objective. Grace appealed to the Federal Circuit for relief.

Appellate court drills down

When interpreting patent claim terms, courts must determine how a skilled artisan in the relevant field would understand the term in the context of the entire patent, including the specification (which includes a written description of the claimed inventions). The Federal Circuit has stated that the specification is the single best guide to a disputed term’s meaning. Courts consider a patent’s prosecution history, too.

The patent’s claims, specification and prosecution history are referred to as “intrinsic evidence.” A court also can rely on a dictionary definition, a type of “extrinsic evidence,” if it doesn’t contradict any definition found in or ascertained from a reading of the patent documents.

If a term’s meaning is clear from the intrinsic evidence, though, there’s no need to resort to extrinsic evidence. Such was the case here, the Federal Circuit said.

The intrinsic record informed a skilled artisan the “enlarged chamber” is large enough to contain enough sample fluid that it doesn’t fall into the viscometer’s testing section — so that measurement errors common to earlier viscometers won’t occur. Thus, in the context of the patent, “enlarged chamber” didn’t require the chamber to be larger than some baseline object but instead large enough to accomplish a particular function.

The Federal Circuit found both the specification and the prosecution history supported this understanding. Yet the trial court relied on dictionary definitions that contradicted the scope and meaning of the term that a skilled artisan would ascertain by reading the intrinsic record.

More digging required

The Federal Circuit vacated the lower court’s determination that “enlarged chamber” was indefinite and the related invalidity determination. It then returned the case to the trial court for further proceedings.