In short, ConvaTec's patent was a method of making light-stabilised silverised antimicrobial materials for the silverisation of gel-forming fibres in wound dressings. This was a three-step method, of which the third step involved subjecting gel-forming fibres to a binding agent. According to the relevant claim, this agent had to be present in a concentration of "between 1 per cent and 25 per cent". Smith & Nephew made its own range of wound dressings in accordance with method described in the patent, except that it used a concentration of binding agent of no more than 0.77 per cent -- which even a fictional cat can see is not in the range of 1 to 25. Said ConvaTec, this still infringed because, in a scientific context, the standard practice was to express numerical values to a particular degree of accuracy; using the standard rounding convention, the number five was always rounded up. On this basis "between 1 per cent and 25 per cent" encompassed all concentrations greater than or equal to 0.5 per cent and less than 25.5 per cent. No, said Birss J: the range was to be interpreted on the basis of significant figures, not rounding to the nearest whole number, so that the claim included concentrations greater than or equal to 0.95 per cent and less than 25.5 per cent (on that basis he held that, while the 0.77-based process did not infringe the patent, an earlier process did). This decision didn't seem to make anyone very happy, so both parties appealed.
Allowing Smith & Nephew's appeal and
* The approach to be adopted when interpreting claims that contained a range of numbers was the same as that to be adopted in relation to any other patent claim: the court had to be objective, asking what a skilled person would have understood the patentee to mean. The claims were to be construed purposively and in context [while the court cited more modern precedents, this Kat was pleased to see Catnic Components v Hill & Smith Ltd  RPC 183 (HL), getting a mention: that's where "vertical" was generously construed as being a full six degrees off perpendicular].
* Where a numerical range was being construed, the question was what the person skilled in the art would understand the numerals to mean, in the light of common general knowledge as well as the context of the specification as a whole.
* Would that skilled person understand that the patentee had expressed the numerals to a limited degree of precision so as to include all values falling within the claimed range when stated with the same degree of precision? That would depend on all the circumstances, including the number of decimal places or significant figures to which the numerals were expressed.
|Waiting for Bond ...|
* Secondly, would the skilled person understand the numbers to be expressed as whole numbers or in terms of significant figures? There was no logical basis for preferring significant figures approach [if you've ever wondered what is significant about significant figures, take a look at the quote in para 24: to the scientist there is a difference between 1.3 and 1.30 ...]. Here ConvaTec sought to convey the range of permissible binding agent concentrations and the accuracy with which those concentrations had to be determined. The skilled person would understand the 1 per cent and 25 per cent limits to have been expressed to the nearest whole number and the trial judge should therefore have found that the skilled reader would understand that ConvaTec intended the claim to embrace all concentrations of binding agent greater than or equal to 0.5 per cent and less than 25.5 per cent.
Book of Numbers here and here