The earlier case of Catnic Components Ltd. v Hill & Smith Ltd., Lord Diplock had established the principle that patents were to be read in a "purposive" manner.
The question to be answered in establishing infringement, as formulated by Lord Diplock, was a complex, multi-part enquiry.
The variant will not infringe if any of the following are true: In the Improver case, the patent covered a depilatory device having a curved "helical spring" driven by a motor.
The judge answered the three questions as follows: (i) the change to a rubber rod had no material effect on the way the invention worked; and (ii) it would have been obvious to an expert that the rubber rod would work in the same way; but (iii) the expert would have understood from the patent that the patentee meant to confine his claim to a "helical spring", in its primary meaning and not in a wide generic sense.
[1]The current position, therefore, is that the House of Lords has held that the principle of purposive construction is entirely in accordance with the Protocol to Article 69, but that the Improver questions may not represent the best approach for dealing with every infringement issue.