By Ryan Tucker
Patent attorneys spend a great deal of time trying to find the ‘perfect’ word for a technical element of an apparatus or method in patent applications. They are required to conduct the same analysis for numerical limitations, including, numerical ranges. The construction of both words and numerals needs to take place in patent attorneys’ daily practices; with the latter equally applying to all fields of technology: Electrical, chemical, mechanical, biotechnological, etcetera.
Using Smith & Nephew Plc v ConvaTec Technologies Inc  EWCA Civ 607, this article will examine numerical limitations in patent claims in the United Kingdom (UK) (and by implication, South Africa (SA)), given their impact on patent drafting and prosecution, as well as on patent enforcement/litigation.
Facts of the case
The critical issue for the court was deciding the numerical limits of the first claim of ConvaTec’s UK method Patent No. 1, 343, 510, entitled ‘Light Stabilized Antimicrobial Materials’ (the patent). This contained a third integer, which read –
‘(c) subjecting said polymer, during or after step (b) to one or more agents selected from the group consisting of ammonium salts, thiosulphates, chlorides and peroxides which facilitate the binding of said silver on said polymer [the agent being present in a concentration between 1% and 25% of the total volume of treatment], which material is substantially photostable upon drying, but which will dissociate to release said silver upon rehydration of said material.’
Smith & Nephew had developed a process that it thought would not infringe the patent, by changing the concentration of binding agent to no more than 0,77%, and this required an interpretation of the numerical limitations of the bracketed phrase in the above integer.
In a nutshell: Did Smith & Nephew’s ‘modified process’ infringe on NovaTec’s patent, which allowed for a range, namely, between 1% and 25%?
Court of Appeal’s judgment
The Court of Appeal dealt, ultimately, with one principal issue: The correct construction of the phrase ‘the agent being present in a concentration of between 1% and 25%.’
The court began its assessment by restating the approach to interpretation of patent claims as considered by Lord Hoffman in Kirin-Amgen Inc v Hoechst Marion Roussel Ltd & Ors  UKHL 46.
As explained, interpretation of claims is objective and the question is always ‘what would a skilled person have understood the patentee’s words (or numerals) to mean?’
Furthermore, Lord Hoffman’s principles were summarised by Jacob L.J. in Virgin Atlantic Airways Ltd v Premium Aircraft Interiors UK Ltd  EWCA Civ 1062 at para 5 as follows:
The court went on to say that the above principles are just as applicable to a claim containing a numerical range or limitation as they are to one containing words or phrases. In the UK (as in SA), the objective of art 69 is achieved by ‘contextual interpretation’ or ‘purposive construction’, namely, what would a skilled person have understood the words (or numerals) to mean?
The court emphasised three possible ways to construe numerical values in a claim:
The court affirmed the court a quo’s rejection of Smith & Nephew’s primary case, that the limits of the claim be the range exactly between 1% and 25%. This left the court in no doubt that a skilled reader would not believe that this is how the patentee intended the claim limits to be understood. Instead, a skilled reader would believe that the patentee intended the limits to be understood in a less precise way.
Number rounding vs significant figures approaches
The court went on to discuss the ‘number rounding’ or ‘whole number’ approach.
At the bottom of the range, 1% includes all those values, which round to 1% when expressed to the nearest whole number. At the top of the range, 25% includes all those values, which round to 25% when expressed to the nearest whole number. Looking at the claimed range as a whole, it embraces all values greater than or equal to 0,5% and less than 25,5%.
The court held the ‘significant figures’ approach to be a little more complex, summarising the relevant rules as follows –
‘i) non-zero digits are always significant;
iii) leading zeros are never significant …; and
Taking first the bottom of the range, 1%, and the top of the range, 25%, there is asymmetry around these numbers (in relation to ‘1’ – greater than or equal to 0,95% and less than 1,5%; and ‘25’ – greater than or equal to 24,5% and less than 25,5%).
The court opined that the ‘significant figures’ approach gives rise to ‘very strange results if applied to the teaching in the body of specification’, citing examples from ConvaTec’s diagrams. On the contrary, the ‘number rounding’ approach produces a symmetrical distribution of random errors around a number (namely, ‘1’ incorporates all values greater than or equal to 0,5% and less than 1,5%).
The court stated that there can be no logical basis for preferring the ‘significant figures’ approach over the ‘whole number’ (or zero decimal place) approach in interpreting numerals in claims, ultimately siding with ConvaTech’s view that it is not the number of significant figures that is important in this context, but the precision with which the number is written.
In this judgment the UK Court of Appeal has shown a preference for the ‘number rounding’ approach over the ‘exact values’ and ‘significant figures’ approaches, unless the description of the specification indicates expressly otherwise.
However, the ‘number rounding’ approach, although simple to apply when construing numerical limitations and ranges, is not without its weaknesses. In this case, the result lead to 0,5% being the lowest value to be below (relative to the number ‘1’) in order to overcome the patent, which is a relatively large margin to overcome (0,5%), in my view.
Other foreign jurisdictions may interpret numerical ranges and limitations differently. Therefore, there is the possibility for variation in solutions on the same inquiry – territory by territory. This is important to take into account, as South African courts, driven by the constitutional imperative, may refer to any foreign judgments in its own assessment of a particular case. This is of particular relevance in intellectual property (including patent) matters.
Ryan Tucker BSc Genetics Developmental Biology Microbiology Biotechnology LLB (Wits) is an attorney at RM Tucker Attorneys in Johannesburg.
This article was first published in De Rebus in 2016 (Dec) DR 34.