5.5.1 Ambiguous parameters
Where inventions are defined by claims containing unclear features, e.g. ambiguous parameters, which cannot be clarified in the light of the description, the effect sought may be the only means of understanding such inventions. This effect must then be taken into consideration and assessed under Art. 83 EPC with a view to establishing whether the invention can be reproduced (see T 862/11).
According to T 1845/14 (two contradictory definitions of a parameter): The ambiguous definition of a parameter in a claim may result in the scope of the claim to be broader than the patentee might have intended. In such a case the question arises whether the teaching of the patent in suit, which was directed to the claimed subject-matter having regard to a specific meaning of that parameter (which, however, was omitted), would nevertheless have enabled the skilled person to carry out the invention outside of the scope intended by the patentee, using common general knowledge and a reasonable amount of experimentation.
In T 1845/14 the board stated that the invention for which sufficiency of disclosure had to be assessed is defined by the terms of the claims, whose meaning had to be construed in view of the ambiguous definition of the parameter (CDBI). Following the normal rule of claim construction, terms used in a claim, such as parametric definitions, should be given their broadest technical sensible meaning in the context in which they appear and having regard to the common general knowledge. Concerning the CDBI, there was no evidence that it had a recognised meaning in the art at the priority or filing date of the patent in suit and the contradiction between the two definitions of it provided in the specification could not be resolved. Thus, this wording must be broadly construed to cover both definitions provided in the specification. Then the ambiguous definition of a parameter in a claim may result in the scope of the claim to be broader than the patentee might have intended. It was undisputed that the whole teaching provided in the specification related to only one definition of CDBI provided in the specification. Even accepting that the teaching was sufficient for one of the two definitions, the patent proprietor did not indicate how the skilled person, based on their common general knowledge, would have been in a position to complement the teaching contained in the patent in suit to prepare with reasonable effort the copolymers in accordance with the second definition of the CDBI which did not belong to the group of polymers in accordance with the first definition of CDBI. The subject-matter of claim 1 has not been shown to be enabled in the whole range claimed, and the main request was refused (Art. 100(b) EPC).
In T 482/09 (viscosity) the boards held that, in opposition and any ensuing appeal proceedings, the result of using such an indefinite term in a claim was that it could not be taken to determine the limits to the protection sought, so that novelty and inventive step had to be assessed in the light of the prior art identified on the basis of all its technically meaningful possible interpretations. If the term had no specific meaning whatsoever, it would even lose entirely its effect of delimiting the claimed subject-matter from the relevant prior art.