In Smith & Nephew v. ConvaTec [2015] EWCA Civ 607 in July 2015 the Court of Appeal provided guidance on interpretation of numbers in claims, which (like words) must be construed. The case has application in all fields/industries, including electrical/electronics and communications.

Background

ConvaTec's patent claim required a binding agent present "in a concentration of between 1% and 25%". Smith & Nephew had developed a process at a concentration of no more than 0.77%. Three competing constructions of the claim were argued at trial and appeal:

  • an "exact values" approach: so that anything below "1" does not infringe;
  • a "significant figures" approach: so that "1" to one significant figure includes all values ≥ 0.95 and < 1.5 with the result that 0.77 does not infringe; and
  • a "number rounding" approach: so that "1" includes all values ≥ 0.5 and < 1.5 with the result that 0.77 infringes.

The trial judge applied the significant figures approach and held there was no infringement. The Court of Appeal reversed that, applying the number rounding approach and finding infringement.

Law on claim construction as applied to the case

Article 69 of the European Patent Convention provides that: "The extent of the protection conferred by a European patent shall be determined by the claims. Nevertheless, the description and drawings shall be used to interpret the claims". The Protocol on Interpretation of Article 69 provides that claims must be construed so as to "combine fair protection for the patentee with a reasonable degree of legal certainty for third parties". In the UK, this goal is achieved by "purposive construction", asking what a skilled person would have understood the patentee to be using words in the claim to mean. The Court of Appeal confirmed "purposive construction" applies to numbers in claims too, using the description to aid that interpretation.

Significant figures were not used consistently throughout ConvaTec's patent, but neither were decimal places. The Court of Appeal noted that although the purpose of expressing numbers to a particular degree of precision is to convey to the reader the degree of accuracy with which a measurement or calculation has been made, the purpose of numerical ranges in claims is to convey the range of permissible concentrations and the accuracy with which those concentrations need to be determined. It noted that the significant figures approach leads to an asymmetry around the number 1 (≥ 0.95 to <1.5) which bears no relation to the symmetrical distribution of random errors around a number whereas number rounding is symmetrical ("1" includes all values ≥ 0.5 and < 1.5). This appeared to influence the Court of Appeal and lead it to prefer to treat the numbers in claim 1 as stated to a number of decimal places, rather than to a number of significant figures. The numerical range "1 to 25%" was therefore construed as including values ≥ 0.5 and < 25.5%, rather than including values ≥ 0.95 and <25.5%. Though this construction meant 0.5% fell within the range of "1 to 25%", the Court of Appeal said the skilled person would accept this as the inevitable consequence of ConvaTec adopting such a wide range of permissible concentrations.

Comments and conclusions

Each case will turn on the facts and how numbers are presented in the patent claims and description, but the UK Court of Appeal has shown a preference for construing the limits of numerical ranges using number rounding, rather than significant figures, and the trial courts may follow that unless it is clear from the description that some other approach should be used.

The number rounding approach has the benefit of being easy to apply when assessing the limits of a claimed range. However, it would require something to be below 0.5 to avoid a claim starting from "1", which is a large relative margin. Construing claims by number rounding is not a convention applied universally across Europe, so there is the potential for different answers on the same question of infringement of numerical ranges, country by country. When the Unified Patent Court opens, it will need to consider the differing approaches in Europe when developing its own case law on construction of numbers in claims.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.