A patent specification is addressed to a person skilled in the relevant art of the specification. This person brings their understanding of the terminology and workings of the art to the construction of the specification. Lord Shaw in B.T.H. v Corona Lamps 39 RPC 49 stated:

"A specification must take its rank among all ordinary documents which are submitted to a reader for his guidance or instruction, and a reader ordinarily intelligent and versed in the subject matter. Such a reader must be supposed to bring his stock of intelligence and knowledge to bear upon the document, not unduly to struggle with it, but anyhow to make the best of it."

Thus, the specification is to be construed in the light of the common general knowledge in the relevant art at the priority date of the application. As stated in Welch Perrin v Worrel (1961-62) 106 CLR 588 at 610:

"If it is impossible to ascertain what the invention is from a fair reading of the specification as a whole, that, of course, is an end of the matter. But this objection is not established by reading the specification in the abstract. It must be construed in the light of the common general knowledge in the art before the priority date."

See also Decor Corp v Dart Industries 13 IPR 385 and Melbourne v Terry Fluid Controls Pty Ltd (1994) AIPC 91-058

A full discussion of a number of relevant decisions on this subject is given in Valensi & Another v British Radio Corporation (1973) RPC 337. In particular, at page 377:

"We think that the effect of these cases as a whole is to show that the hypothetical addressee is not a person of exceptional skill and knowledge, that he is not expected to exercise any invention nor any prolonged research inquiry or experiment. He must, however, be prepared to display a reasonable degree of skill and common knowledge of the art in working trials and to correct obvious errors in the specification if a means of correcting them can readily be found."

The Valensi case (supra) should be read in the light of the observation in American Cyanamid Company v Ethicon Limited [1979] RPC 215 at page 245, to the effect that:

"... many of those involved and taking part in the placing on the market of such a new product, which was artificial and had no previous equivalent in this respect, would be highly qualified scientists trained at least to university standard, with all that entails, and used to carrying out chemical and biological research work in research departments. That is what in fact happened in the case of both the plaintiffs' and the defendants' artificial sutures here, and it would ... be highly misleading to suggest that there was in fact, in the present case, any body of 'intermediately' skilled technicians to whom the specification could be addressed whose existence must be assumed to be 'obvious', as was assumed by the Court of Appeal in the Valensi case (1973) RPC 337. The correct view ... which is consistent with the principle which the Court of Appeal must ... be presumed to have acted upon, is to hold as matter of law ... that the answer to the question: "Who is the skilled addressee of the specification?", depends upon making an examination of the facts of each case, and in so doing regard must be paid primarily to the nature of the invention, to the nature and size of the industry concerned, and the way it is organised for the purposes of conducting research into and of producing and marketing its products."

The position in Australia is no different from that in the UK. In Universal Oil Products v Monsanto (1972) 46 ALJR 658 Gibbs J. stated:

"The specification is sufficient if the patentee makes the nature of his invention, and how to perform it, clear and intelligible to persons having a reasonably competent knowledge of what was known before on the subject to which the patent relates, and having reasonably competent skill in the practical mode of doing what was then known."