In Ultimax Cement Mfg. Corp. v. CTS Cement Mfg. Corp., the Court of Appeals for the Federal Circuit (“CAFC”) reversed and remanded a finding of noninfringement by the District Court for the Central District of California, citing an incorrect claim construction. The CAFC also reversed a holding of indefiniteness by the District Court finding the lower court applied the incorrect standard.

Ultimax sued CTS for infringement of U.S. Patents No. 4,957,556 (“the ’556 patent”) and 6,113,684 (“the ’684 patent”), both pertaining to rapid-hardening, high-strength cement. Ultimax alleged infringement of claims 9-11 of the ’556 patent and claim 17 of the ’684 patent. The CAFC reversed the District Court’s interpretation of ’556 patent claim language and held the lower court misapplied the indefiniteness standard regarding the ’684 patent.

The ’556 Patent

In finding CTS did not infringe the ’556 patent, the District Court construed the claim term “CaSO₄ anhydride,” also known as “soluble calcium sulfate anhydride.” The District Court defined “anhydride” using a single dictionary’s definition as “a compound formed from an acid by removal of water.” The District Court reasoned that if the claim drafters had intended to refer to calcium sulfate from which water has been removed, which they did, they would have use the term “anhydrous” or “anhydrite.” The District Court acknowledged the observations of a neutral expert who believed that one skilled in the art might recognize that the drafters intended the claim to refer to “anhydrite” rather than “anhydride.” However it held it could not substitute terms as that would amount to redrafting the claims. Thus, according the District Court’s interpretation, the claim term “soluble CaSO₄” necessitated that the compound include not only calcium sulfate, but also an acid from which water had been removed. Because CTS’s cement did not contain an acid from which water had been removed, the District Court granted CTS’s summary judgment motion for noninfringement.

Reviewing the District Court’s decision de novo, the CAFC began its analysis by looking to the language of the claims themselves, which are read in view of the specification. The CAFC made special note that a claim should not rise or fall based upon a specific dictionary definition as it does not necessarily reflect the inventor’s goal of putting forth his invention as a person of ordinary skill in the art would understand it. The CAFC reasoned that the term “anhydride” when placed next to “CaSO₄” was intended as a modifier to term “CaSO₄” and thus referred to calcium sulfate from which any associated water had been removed. The CAFC found support for this reasoning in multiple dictionaries, which allow “anhydride” to refer to a compound other than one obtained by removing water from acid, based on context. Further, the CAFC noted that word “anhydride” never appeared alone in the specification, but only as a modifier of “calcium sulfate.” Finally, the CAFC held that, contrary to the District Court’s conclusion, interpreting the claim term as the neutral expert had suggested would not be rewriting the claim or correcting a typographical error. The CAFC reasoned that the drafters could not have intended the claim term as understood by the District Court because such a reading would have been redundant. The CAFC noted that even the defendant, a person of at least ordinary skill in the art, used the term “anhydride” when they meant “anhydrite,” with no resulting confusion. In reversing the District Court’s holding, the CAFC construed the term “soluble CaSO₄ anhydride” to mean “soluble anhydrous CaSO₄,” or “soluble anhydrous calcium sulfate.” Because of this reversal, the CAFC vacated the District Court’s holding of noninfringement and remanded the issue to the District Court.

The ’684 Patent

The District Court had held claim 17 of the ’684 patent was indefinite and granted summary judgment to CTS. The District Court found claim 17 to be indefinite based on its recitation of the formula “(C,K,N,M)₄(A,F,Mn,P,T,S)₃(cl,S)” which is referred to as crystal X in the specification, and the formula “C₉S₃S₃Ca(f cl)₂.” The District Court reasoned that crystal X is a solid solution in which various elements can be substituted for one another. Based on the testimony of the neutral expert, the ability to substitute yields 5,000 different crystal X compounds. The District Court did not limit crystal X to a single compound and held that it was overly broad and thus indefinite. The District Court also held the claim indefinite because it lacked a comma between “f” and “cl,” indicating that both fluorine and chlorine needed to be present in the claimed compound. The District Court declined to correct the error holding that it was not apparent on the face of the patent despite the fact that both the District Court itself and the expert recognized the clear need for a comma between “f” and “cl.”

The CAFC reversed the District Court’s finding of indefinateness holding that even if crystal X is construed to be as broad as the District Court found, it is not insolubly ambiguous and that the notation “(f cl)” must be viewed as one of ordinary skill in the art. The CAFC reasoned that claim indefiniteness is dependent upon whether those skilled in the art would understand what is claimed. The CAFC held that a claim to a formula containing over 5000 permutations is not necessarily ambiguous if it sufficiently notifies the public of the scope of the claim. While broad, the claim was not insolubly ambiguous, nor did it prevent the public from understanding the scope of the patent. The CAFC also held that the District Court failed to view the “(f cl)” notation as one of ordinary skill in the art. While District Courts cannot rewrite a claim to correct a material error, they may correct an obvious typographical error so long as: 1) the correction is not subject to reasonable debate to one of ordinary skill in the art and 2) the prosecution history does not suggest an alternative interpretation. The CAFC reversed the District Court’s summary judgment ruling regarding claim 17 relying on the District Court’s own observations, the testimony of the neutral expert and the determination that “C₉S₃S₃Ca(f cl)₂” corresponds to no known mineral. The CAFC concluded by directing the District Court to enter summary judgment that claim 17 is not indefinite based on either formula.