UK Claim Construction: Numerical Limitations

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 a "number rounding" approach: so that "1" includes all values ≥ 0.5 and 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...