Clarity: Is it usual, or is it not usual: that is the question.
Although a product may be defined in a claim in various ways, the Guidelines for Examination in the European Patent Office (hereinafter: “the Guidelines”) state that a product should only be exceptionally defined by its parameters. In this context, parameters are considered to be characteristic values, which may be values of directly measurable properties or may be defined as more or less complicated mathematical combinations of several variables in the form of formulae.
However, according to the Guidelines, such a characterization by parameters is in principle only allowable in those cases where the invention cannot be adequately defined in any other way. Additionally, it is required that the parameters can be clearly and reliably determined either by indications in the description or by objective procedures, which are usual in the art. Given that the definition of the invention should appear completely in the claim itself whenever reasonably practicable, and given that the method of measurement is necessary for the unambiguous definition of the parameter, the method should be mentioned in the claim.
There are only three exceptions to the general rule that the method of and means for measurement of the parameter must be included in the claim, namely:
(i) The description of the method is so long that its inclusion would make the claim unclear through lack of conciseness or difficult to understand (in which case the claim should include a reference to the description);
(ii) A person skilled in the art would know which method to employ, e.g. because there is only one method, or because a particular method is commonly used; or
(iii) All known methods yield the same result (within the limits of measurement accuracy).
In all other cases the method of and means for measurement should be included in the claims, as the claims define the matter for which protection is sought.
Further, while parameters can meet the requirement of clarity, the foregoing is only true for parameters which are considered “usual” by the skilled addressee. In contrast, cases in which unusual parameters are employed or a non-accessible apparatus for measuring the parameter(s) is used are prima facie objectionable on grounds of lack of clarity, as no meaningful comparison with the prior art can be made.