The ConvaTec patent covered any salt solution “between 1 per cent and 25 per cent of the total volume of treatment”. However, Smith and Nephew devised a competing product that used 0.77 per cent concentration, bypassing, or so it believed, the ConvaTec patent.
A previous judgment in 2013 ruled in Smith & Nephew’s favour because of a mathematical quirk known among chemists as the “significant figures rule”, which is a way of taking into account errors of measurement.
This judgment ruled that the patent covered any solution greater than or equal to 0.95 per cent and less than 25.5 per cent, which meant Smith & Nephew was free to flog its multi-million pound products without paying anything to ConvaTec.
So in this earlier judgment “one” meant anything greater than or equal to 0.95 and less than 1.5, which produced an uncomfortable asymmetry that did not go unnoticed in last week’s judgment. How could “one” include something that is 0.05 less but also include something that is nearly ten times this figure more – for instance 0.49 more than 1?