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5.108 Parametric claims comprise definitions of specific parameters, such as directly measurable physical properties or mathematical combinations of several variables in the form of formulae. At first instance, the key consideration for such claims is likely to be novelty (see Section K in Chapter 3).
5.109 With respect to clarity, the consideration for such claims is whether the specified parameters would introduce ambiguity to the scope of the claims to the extent that no meaningful comparison with the prior art can be made. If it is considered unclear to the skilled person which products do indeed possess the parameters required and therefore would fall within the scope of the claims, a lack of clarity objection should be raised. For example, applications in which non-accessible apparatuses are used for measuring the specified parameter(s) are prima facie objectionable on grounds of lack of clarity, as no meaningful comparison with the prior art can be made. Such applications might also disguise a lack of novelty. A clarity issue may also arise in the event where the scope of the claimed subject matter might vary when different measurement methods are used for characterizating the specified parameters. In principle, a clear disclosure in the specification of the measurement method is necessary for the unambiguous definition of the parameter, unless a person skilled in the art would know what method to use (e.g. because there is only one method, or because a particular method is commonly used) or all known methods would yield the same result. It is generally considered unnecessary to recite the method of and the means used for the characteriziation of the specified parameters in the claims; however, such characterization methods and means should be clearly determined by the skilled person when reading the specification as a whole.
5.110 Depending on the facts of the case, parametric claims are in effect claims by result which may be subject to lack of support/sufficiency objections. The usual considerations are whether the claims encompass matter that owes nothing to the teachings of the invention in the specification. If it is considered that the skilled person would be faced with undue burden to arrive at the full scope of the claim by following the exemplification given in the specification or procedures common in the art, a lack of support/sufficiency objection should be raised. Admittedly, there is a delicate balance between the considerations for clarity and lack of support/sufficiency, which have to be assessed based on the facts of each individual case. Objections should not arise merely on the basis that parameters not known in the prior art are used in the claims. In the event it is evident from the specification that the skilled person would face no difficulty in carrying out the characterization disclosed and would be able to establish the exact meaning of the specified parameters (see for example decision T 231/01), use of such parameters would be allowable.