IP & IT Law Bytes: Patents: construction of numerical range in patent claims

By Audrey Horton


The Court of Appeal has allowed an appeal against a finding of non-infringement on the ground that the High Court had wrongly construed the numerical range in the claims of a patent.


Article 69(1) of the European Patent Convention (EPC), and the Protocol on the Interpretation of Article 69, provide that the extent of the protection conferred by a European patent or application is determined by the claims. However, the description and drawings may be used to interpret the claims.


C owned a European patent concerned with the silverisation of gel-forming fibres (the patent). S applied to revoke C’s patent.

The High Court held that the patent was valid. S appealed.

The Court of Appeal dismissed the appeal.

S then developed a new process and applied for a declaration of non-infringement of the patent. C counterclaimed alleging infringement.

The High Court held that S’s new commercial product did not infringe the patent, but that work done in developing the new product, which was used to generate data for use in the application for regulatory approval, did infringe. The decision was based on using the significant figures construction of a term used in the claims: "the agent being present in a concentration between 1% and 25% of the total volume of treatment". According to this construction, 1% was a number stated to one significant figure, putting the lower limit at 0.95% (the lowest number that rounded up to 1 as one significant figure), and the upper limit at less than 25.5% (25% was a number stated to two significant figures).

Both parties appealed. S relied on the significant number approach and C put forward the whole number (or zero decimal places) approach.


The court allowed C’s appeal and dismissed S’s appeal.

The approach to the interpretation of claims containing a numerical range was the same as that to be adopted in relation to any other claim but there were certain relevant principles.

The scope of numerical range claims was exactly the same whether considering infringement or validity.

Rounding or any other kind of approximation could not be used to change the disclosure of the prior art or to modify the alleged infringement.

The meaning and scope of a numerical range in a patent claim had to be determined in light of the common general knowledge and in the context of the specification as a whole. It might be the case that, in light of the common general knowledge and the teaching of the specification, the skilled person would understand that the patentee had chosen to express the numerals in the claim to a particular but limited degree of precision and so intended the claim to include all values which fell within the claimed range when stated with the same degree of precision. However, whether that was so or not would depend on all the circumstances including the number of decimal places or significant figures to which the numerals in the claim appeared to have been expressed.

The correct construction here was the whole numbers approach, which meant that the skilled reader would understand that S, by specifying a range of between 1% and 25%, intended the claim to embrace all concentrations of binding agent greater than or equal to 0.5% and less than 25.5%. So, S’s new commercial product (at 0.77%) infringed the patent.


This decision provides guidance on the interpretation of the scope of numerical ranges in a patent claim. The issue of how far outside those exact numbers the scope of the claim extends has to be determined using the general principles of patent construction, taking into account how the skilled reader would understand the numerical range. One factor that influenced this decision was that the specification used different levels of accuracy in numbers used, which the court saw as an indication that the limits expressed in the claims were deliberately chosen. The decision also illustrates how difficult it can be in practice to interpret the scope of a numerical range in a patent claim in order to determine whether or not that claim is infringed.

Case: Smith & Nephew plc v Convatec Technologies Inc [2015] EWCA Civ 607.

First published in the August 2015 issue of PLC Magazine and reproduced with the kind permission of the publishers. Subscription enquiries 020 7202 1200.