When undefined parameters are used in the claims and no details of the measuring methods are supplied, the question arises whether there is a problem with respect to Art. 83 or Art. 84 EPC. The answer to this question is important because in opposition proceedings the patent can be examined for its compliance with Art. 83 EPC without any restriction. Compliance with Art. 84 EPC is however examined only in cases where there has been an amendment.
In some decisions (for example, T 123/85, T 124/85, T 172/87, T 358/88, T 449/90, T 148/91, T 267/91, T 697/91, T 225/93, T 378/97, T 387/01, T 252/02, T 611/02 and T 464/05) the absence of information in the application on methods for measuring undetermined parameters in the application was considered a problem with respect to Art. 83 EPC 1973. These were all inter partes proceedings. This problem has also been addressed with reference to Art. 83 EPC 1973 in ex parte proceedings, (see T 122/89 of 5.2.1991 and T 503/92). Other decisions have considered this a problem with respect to Art. 84 EPC 1973, for example, in T 860/93 (OJ 1995, 47), also ex parte proceedings, it was decided that the absence of methods for measuring a relative quality in the claim was a problem with respect to the clarity of the claim under Art. 84 EPC 1973 (see also T 230/87, T 176/91, T 917/92, T 299/97, T 439/98, T 413/99, T 930/99, T 960/98, T 619/00, T 943/00, T 344/01, T 563/02, T 1033/02, T 208/03, T 882/03, T 452/04, T 1316/04, T 466/05, T 1586/05, T 859/06). Some of these decisions are discussed further below.
According to T 593/09 the requirement of sufficient or "enabling" disclosure in the sense of Art. 83 EPC is different from and independent from the clarity requirement pursuant to Art. 84 EPC, namely that the claims, which define the matter for which protection is sought, "shall be clear and concise". The board saw this distinction as underlying the decision in T 1062/98, where it was held that whether the skilled person is capable of determining whether a certain feature would be infringing a feature claimed is not a matter of sufficiency of disclosure as required by Art. 83 EPC, but a matter to be decided by the national courts. The board in T 1062/98 went on to say that the determination of the scope of the claim relates in fact to the question whether the claims properly define the matter for which protection is sought, which are, however, the requirements imposed by Art. 84 EPC and R. 29(1) EPC 1973 and which do not form grounds of opposition.
The board in T 593/09 thus saw a distinction between the meaning of "clear" in Art. 83 EPC, which concerns the disclosure (the "technical teaching") of the application or the patent on the one hand, and in Art. 84 EPC, where that expression relates to the claims, which "shall define the matter for which protection is sought" on the other hand. In short, there is a distinction between clarity of what has been disclosed and clarity of what is claimed.
The board found that this distinction was not always properly made, in particular in respect of so called "ambiguous parameters", i.e. parameters present in the description and/or claims, whose exact definition and/or applicable measuring method remained doubtful. For example, numerous decisions of the boards of appeal have as a relevant criterion for the sufficiency of a disclosure containing an ill-defined parameter, whether the skilled person knows if he is working within or outside of the scope of the claim (e.g. T 256/87; T 387/01; T 252/02 and T 18/08). It was however, not always apparent from the reasoning of these decisions whether or not this criterion was meant to be the sole or the decisive one.
On the other hand, as the board in T 593/09 pointed out, decisions exist that consider the question of whether or not the skilled person knows if he is working within or outside of the scope of the claims not to be a matter of sufficiency of disclosure but rather a matter of Art. 84 EPC (see, e.g. T 396/02 and T 1033/02).
The board in T 593/09 found that it is certainly true that where the disclosure is insufficient within the meaning of Art. 83 EPC due to the presence of an ill-defined parameter, claims defined by reference to this parameter would lack clarity under Art. 84 EPC, since establishing the exact scope of the claim would then be impossible. But that did not allow the reverse conclusion to be drawn, namely that there is insufficient disclosure within the meaning of Art. 83 EPC whenever the scope of the claims is unclear, i.e. not properly defined.
In T 464/05, the board held that the patent in suit did not disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art (Art. 83 EPC 1973). This finding essentially corresponded to the requirement that the skilled person had to know "when he is working within the forbidden area of the claims" (see e.g. decisions T 256/87 and decisions T 387/01, T 611/02 and T 252/02 of board 3.2.06). In the board's view, although this requirement in its broad reading was certainly related to Art. 84 EPC 1973 (see e.g. decision T 943/00), it was in fact related to Art. 83 EPC 1973 in its restricted reading, implying that the skilled person had to be able to determine whether a particular object fell within the forbidden area of the claims intended as the area including those embodiments that effectively solved the technical problem underlying the patent in suit.
In T 1055/92 (OJ 1995, 214) the examining division had rejected the patent application under Art. 84 EPC 1973 because in the claim it was not clear how certain values were to be computed. The board held that the requirements of Art. 84 EPC 1973, that the claims shall define the matter for which protection is sought, should be clearly distinguished from the requirement under Art. 83 EPC 1973 that the European patent application had to disclose the invention in such a way that it enabled a person skilled in the art to carry out that same invention. Under Art. 83 EPC 1973, sufficient disclosure was required of a European patent application, i.e. of the application as a whole, comprising the claims, together with the description and the drawings, but not of an individual claim as such. A claim, on the other hand, had to comprise the essential features of the invention (T 32/82, OJ 1984, 354); the essential features should comprise those features which distinguished the invention from the closest prior art. The primary function of a claim was to set out the scope of protection sought for an invention, which implies that it is not always necessary for a claim to identify technical features or steps in detail (see also T 713/98, in point 7.1 above).
According to T 882/03, slightly varying results obtained when using different mathematical models for the calculation of the intrinsic viscosity did not prevent a person skilled in the art from carrying out the invention but were rather related to the question of whether the matter for which protection was sought was sufficiently defined in accordance with Art. 84 EPC 1973.
In T 256/87 (see also point 5.6.5 above), the board had found that the skilled person reading the specification should be able to carry out the invention in all its essential aspects and know when he is working within the forbidden area of the claims. Indirect empirical investigation referred to in the specification was an acceptable solution, which sufficed to fulfil the requirements of Art. 83 EPC 1973 without undue burden. In T 943/00, the board disagreed with T 256/87, finding that the concept of 'forbidden area' was associated with the scope of the claims, i.e. Art. 84 EPC 1973, rather than with sufficiency of disclosure. The board in T 466/05 agreed, also stating that a distinction should be made between the requirements of Art. 84 EPC 1973 and those of Art. 83 EPC 1973, and that with respect to sufficiency, the relevant question was whether the patent in suit provided sufficient information which enabled the skilled person when taking into account common general knowledge to reproduce the invention. See also T 452/04 and T 1586/05. Other decisions have also interpreted the statement, 'knowing when working within the forbidden area of the claims' formulated in T 256/87 as addressing the question of the limits of protection conferred by the claims, and thus relating to a requirement of Art. 84 EPC 1973 rather than of Art. 83 EPC 1973 (e.g. T 960/98, T 943/00, T 619/00, T 452/04, T 466/05).
The board in T 608/07 found the issue before it with regard to sufficiency of disclosure was quite similar to the situation in T 256/87, both concerning an insufficiency which arose through ambiguity. Although the board accepted that, depending upon the circumstances, such an ambiguity might very well lead to an insufficiency objection, it should be borne in mind that this ambiguity also related to the scope of the claims, i.e. Art. 84 EPC 1973. Since, however, Art. 84 EPC 1973 was in itself not a ground of opposition, care had to be taken that an insufficiency objection arising out of an ambiguity was not merely a hidden objection under Art. 84 EPC 1973. The board was convinced that, for an insufficiency arising out of ambiguity, it was not enough to show that an ambiguity existed, e.g. at the edges of the claims. It would normally be necessary to show that the ambiguity deprived the person skilled in the art of the promise of the invention. It went without saying that this delicate balance between Art. 83 and 84 EPC 1973 had to be assessed on the merits of each individual case.
According to T 593/09, the same rationale underlay both T 608/07 and T 815/07 (and also Kirin-Amgen Inc v. Hoechst Marion Roussel Ltd  UKHL 46 of the United Kingdom House of Lords); namely, where a claim contains an ill-defined ("unclear", "ambiguous") parameter and where, as a consequence, the skilled person would not know whether he was working within or outside of the scope of the claim, this, by itself, is not a reason to deny sufficiency of disclosure as required by Art. 83 EPC. Nor is such a lack of clear definition necessarily a matter for objection under Art. 84 EPC only. What is decisive for establishing insufficiency within the meaning of Art. 83 EPC is whether the parameter, in the specific case, is so ill-defined that the skilled person is not able, on the basis of the disclosure as a whole and using his common general knowledge, to identify (without undue burden) the technical measures (e.g. selection of suitable compounds) necessary to solve the problem underlying the patent at issue.
In T 378/97, the board noted that sufficiency of disclosure addressed the practitioner who reduced the invention to practice, but did not stick to any precise theoretical values. Varying results did not, therefore, necessarily prevent a person skilled in the art from carrying out an invention (Art. 83 EPC 1973), but could be a matter of the definition of the invention under Art. 84 EPC 1973. See also T 960/98, where the board stated that the relevant question with respect to sufficiency of disclosure was whether the patent in suit provided sufficient information to enable the skilled person, taking into account common general knowledge, to reproduce the invention, and T 586/94, T 245/98 and T 859/06.
Following T 378/97, the board in T 439/98 found that the appellant's objections in regard to sufficiency of disclosure (the patent in suit allegedly failed to indicate a suitable method for measuring porosity), concerned the scope of the value of porosity indicated in the claim and therefore the clarity of the claim, rather than the possibility of reproducing the invention. In T 619/00, the board agreed that the different methods for determining the value of the gel fraction did not per se represent an undue burden. In the absence of evidence that the different methods specified would lead to determination values deviating from each other by a substantial amount having technical significance (following T 378/97), or by an amount that would place the skilled person in a situation where he was unable to carry out the invention (following T 930/99), the mere fact that the patent specification was silent as to which method should be used did not prejudice sufficiency of disclosure. The question whether the methods defined lead to a unique value or to different values also concerned the clarity of the definition of the subject-matter of the claim under Art. 84 EPC 1973. In T 930/99 only one measuring method was involved and the board had therefore considered T 225/93 inapplicable, (according to T 225/93, different measuring methods which did not always lead to the same result could amount to an undue burden.) The respondent's argument that there would be legal uncertainty, since third parties would not know whether they were working within or outside the range specified, was clearly an argument based on lack of clarity, which was not a ground of opposition and so could not be considered. See also T 396/02.
In T 805/93 the viscosity was the only characterizing feature of the claim at issue and its role in defining the matter for which protection was sought under Art. 84 EPC, was clearly crucial. The lack of information on how the viscosity limit of the claim was to be determined meant the matter for which protection was sought could not be deemed defined, so that the claim did not comply with Art. 84 EPC 1973. In addition, the disclosure of the application in suit did not enable him to carry out the claimed subject-matter on a general basis, so that the requirements of Art. 83 EPC 1973 were also not met. Similarly, in T 431/07, since no method to measure the viscosity was mentioned in the description and due to the numerous methods and devices used to measure viscosity, the information available in the description as originally filed was not sufficient for the person skilled in the art to reproduce the claimed subject-matter under Art. 83 EPC.