3.6. Characterisation of an invention by a parameter

In decision T 94/82 (OJ 1984, 75) the board ruled that the requirement of clarity could be fulfilled in a claim to a product if the characteristics of the product were specified by parameters related to the physical structure of the product, provided that those parameters could be clearly and reliably determined by objective procedures which were usual in the art (see also T 452/91, T 541/97, T 437/98, T 193/01). It is not mandatory to give instructions in the claim itself as to how the product is to be obtained (T 94/82).

In T 849/11 the board summarised case law on the requirements of Art. 84 EPC with regard to the characterisation of an invention by parameters. The board stated that: (i) the claims must be clear in themselves when read by the skilled person, (ii) the method for measuring a parameter (or at least a reference thereto) must appear completely in the claim itself (see T 1156/01, T 412/02, T 908/04, T 555/05, T 1497/08), and (iii) the applicant who chooses to define the scope of the claim by parameters should ensure that a skilled person can easily and unambiguously verify whether they are working inside or outside the scope of the claim. The board further stated that the requirements of Art. 84 EPC can still be met if it can be convincingly shown that: (i) the method to be employed belongs to the skilled person's common general knowledge, or (ii) all the methodologies known in the relevant technical field for determining this parameter yield the same result within the appropriate limit of measurement accuracy (see T 1156/01).

In T 412/02 the board held that the unambiguous characterisation in a claim of a product by parameters or by a mathematical relation between parameters necessarily required that each parameter could be clearly and reliably determined. In the board's view, it followed that the knowledge of the method and conditions of determination of the parameter was necessary for the unambiguous definition of the parameters and, as a consequence, for the unambiguous definition of a mathematical relation between them. Thus, in order to allow the matter for which protection was sought to be defined, it had to be clear from the claim itself when being read by the person skilled in the art exactly how the parameters should be determined. This would, as a rule, imply that the method of determination and the conditions of measurement which might have an influence on the value of the parameter should be indicated in the claim, either expressly or, if appropriate, by way of reference to the description according to R. 29(6) EPC 1973. Such indication would only become superfluous provided it could be shown that the skilled person would know from the outset which method and conditions to employ.

In T 992/02 the board took the view that whilst noting the general principle that the claims must be clear per se, the non-inclusion in the claim of the method whereby one of the parameters characterising the composition claimed (level of formation of volatiles) could be measured was justified by the requirement that the claims be concise. It considered that such a conclusion could be reached in the case in hand because the method was clearly identified in the description and did not give rise to any ambiguity.

In T 29/05 it was found that although different experimental protocols might be applied in the case in point for assessing hybridisation under stringent conditions, they were usual in the art (following T 1084/00).

In T 307/06 the claims contained the added feature "and a T_g of less than 25°C". The board noted that there were different methods for determining T_g (glass transition temperature). However, the mere fact that several methods existed did not render the claims unclear if at least one of the following conditions was met: (a) the different methods yield essentially the same T_g values for the same material, or (b) the person skilled in the art had associated the range of T_g values mentioned in claim 1 at issue with only one standard method of measurement. Neither condition (a) nor (b) was fulfilled. The board concluded that this left doubt as to which subject-matter was covered by claim 1, and thus rendered said claim unclear (see T 728/98, OJ 2001, 319; T 306/13).

In T 1819/07 the board held that the parameter "average particle size" rendered the claim unclear as neither the type of average (volume, surface, number) nor a method for determining it was indicated in the claims. See also T 967/08 and T 45/10.

In T 2086/11 the parameter "mean aspect ratio" represented the mean of the individual aspect ratios, defined as the ratio of the major axis to thickness, of 50 aluminium flake particles having major axes of not more than 10 μm. The board held that this parameter did not enable to distinguish which subject-matter was covered by the claims and which was not. According to the method of measuring explained in the description, the investigated sample contained thousands of particles having a major axis of not more than 10 μm and the method described in the application did not give any precise indication of how to select such 50 particles. One operator, by selecting at random one group of 50 particles, could measure a mean aspect ratio within the claim whilst another operator, by selecting a different group of 50 particles, could find a value of mean aspect ratio outside the claim. The parameter "mean aspect ratio" was thus by itself insufficient to characterise the claimed product in a reliable way and did not comply with Art. 84 EPC 1973.

In T 2676/16 the board disagreed with the examining division that the parameter "an outcome of a pseudo-random hopping" of the method of claim 1 was not clear because it could have many interpretations to a skilled person in the field of telecommunications. In context, the term "outcome" had the same meaning as "result". It was clear that by means of the "pseudo-random hopping" operation a scalar number was to be produced. The meaning of "pseudo-random" was also clear for the skilled reader. The fact that a feature could be implemented in various ways did not necessarily render this feature unclear.

In T 999/20 the application as filed contained no information regarding how the parameter "number average molecular weight" (Mn) specified in the claim was to be determined. However, the board was satisfied that the information provided in the affidavits A1 and A2 showed that the skilled person would know how to determine Mn unambiguously using the standard method (size exclusion chromatography) commonly used in the art. Hence, the Mn feature did not lead to a lack of clarity pursuant to Art. 84 EPC.

In T 1420/21 the board held that the characterising feature "the density of the structures formed on the structured surface ranging between 15% and 80% of the surface" was ambiguous because it did not indicate which of the three surfaces in the claim "the surface" that served as the denominator of the "density" parameter referred to. The claim cited three surfaces: the surfaces of the first or second functional area, the exposed surface and the structured surface.

In T 1726/22 the claimed subject-matter related to an acetylated wood as such; however, it was defined by shrinkage ratios specified in relation to the wood before acetylation. The application did not mention anything regarding how the shrinkage ratios before acetylation could be determined on the basis of the acetylated wood. The board found that it was not enough for the requirement of clarity to be fulfilled that the parameter could be measured when manufacturing the wood, as the manufacturing method was not specified in the claim. It was impossible for the skilled person faced with the acetylated wood to revert to the manufacturing process during which the shrinkage before acetylation could have been measured, or to the unacetylated wood. Even if it was assumed that, as argued by the appellant, the skilled person had the idea to using a reference wood, they would not find any instructions on how to select a suitable reference wood. Considering that the choice of the reference wood, and indeed the choice of the measuring method in general, was in no way limited, it could not be concluded that repeatable and reliable results for the shrinkage ratios would be obtained on this basis, irrespective of the question of whether such a reference wood could be reliably identified, and whether such a reference wood was at all representative of the (acetylated) wood under consideration. The requirements of Art. 84 EPC were therefore not met.