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Parameters at the EPO – avoiding traps for the unwary


Products and processes in the chemistry and material science fields are often defined using parameters. Sometimes a parametric definition is the only way in which to define the property of a substance or in some cases the substance itself. For example, a new crystalline form of a compound is often defined with reference to peak values from an x-ray diffraction spectra. The viscosity of a liquid reactant may be critical to the performance of an industrial synthesis process.

The use of parameters to define a product or process is allowed by the European patent office (EPO) subject to certain conditions, but using parameters can lead to a number of pitfalls and traps for the unwary. Many problems arising from parameters are difficult to overcome after filing because new matter cannot be added to the patent specification. However, these pitfalls can be avoided with an understanding of the EPO’s approach and careful drafting of patent specifications. In this article Zack Mummery will consider the EPO’s approach to parameters in the context of clarity, sufficiency and novelty.


The EPO considers that defining a product or process using a parameter is possible if the parameter can be clearly and reliably determined by objective procedures which are usual in the art. In recent years, the EPO seems to be taking an ever stricter approach to the use of parameters. 

More specifically, the EPO will typically apply the following test to determine whether a claim including a parameter is clear:  

(i) the claims must be clear in themselves when read by the skilled person (not including knowledge derived from the description);

(ii) the method for measuring a parameter (or at least a reference thereto) must appear completely in the claim itself; and

(iii) an applicant who chooses to define the scope of the claim by parameters needs to ensure that the skilled person can easily and unambiguously verify whether they are working inside or outside the scope of the claim. [1]

An ill-defined parameter or the absence of a measurement method for the parameter can be particularly problematic during examination at the EPO. However, both of these pitfalls can be avoided by careful drafting of patent specifications.

Ill-defined parameters

The importance of a clearly defined parameter is highlighted in decision T1819/07 of the Technical Board of Appeal (TBA). The TBA decided that a claim which specified a copper catalyst precursor as having an “average particle size from about 0.1 to about 600 nanometers” was unclear because neither the type of average particle size or the method of determining it was indicated in the claims. The key point in this case was that average particle size could encompass many different types of average having different values, for example arithmetic mean diameter, volume mean diameter or mass mean diameter, so merely reciting “average particle size” was unclear.

Absence of a measurement method

Absence of a measuring method for the parameter is a common pitfall, and in some cases this can be fatal.  This is particularly important for unusual parameters and parameters which can be measured using multiple methods yielding different values.

In cases in which the measurement method belongs to the skilled person’s common general knowledge or multiple measurement methods exist but yield the same result within an appropriate measurement accuracy, then a measurement method may not need to be included in the specification. That said, best practice is always to include a detailed measurement method in the patent specification.

Let’s take distance as an example. Defining an element of an everyday product by its length in cm will likely involve the use of conventional measuring techniques that do not lead to variability in the measured length. In that case, it is unlikely that there will be a need to specify a measurement method in the specification. However, the diameter of microparticles or nanoparticles can depend on the measurement method used, so in that case a detailed measurement method must be included in the specification (e.g. see T 0005/17).

It is important to include a detailed description of the measurement method and to take particular care when the value of the parameter can vary according to the measurement conditions. For example, viscosity is dependent on temperature so a measurement method for viscosity must include the measurement temperature (e.g. see T 0081/13).

It could be tempting to refer to a measurement method by an international standard, for example by specifying an ASTM number. However, such standards may change over time and the standard could omit measurement conditions. Thus, the best approach will always be to include a detailed description of the measurement method in the application, even if the method relates to an international standard.

Unusual parameters

Particular care must be taken when utilising unusual parameters that are not commonly used in the field of the invention. EPO Examiners may often be suspicious that such parameters are being used to mask a lack of novelty over a known product or process.

In the case that the unusual parameter measures a property of a product or process for which there is already a recognised parameter, then the application must state how the unusual parameter is converted to the recognised parameter, or the application must include detail of an accessible apparatus for measuring the parameter. If either of these are missing, then the Examiner is likely to consider that the claims lack clarity.

In the case that the unusual parameter measures a property of a product or process that had not previously been measured in the field of the invention, then the application must clearly define the parameter and  include a description of the measurement method. The EPO tends to be less suspicious of this type of unusual parameter.

Other common clarity issues

While it is acceptable, subject to the conditions above, to define a product by a parameter, care must be taken to ensure that the independent claims include sufficient structural features such that the claims do not merely define a result to be achieved or the underlying technical problem. For example, defining a multilayer polymeric film by its tensile strength without specifying the structural features leading to the tensile strength will likely prompt a result to be achieved type objection at the EPO. Similarly, the EPO may also consider that such a claim lacks essential technical features, meaning that the claim is unclear.   


If the only feature distinguishing a claimed product or process from the prior art is the value of a parameter, then during examination the burden of proof will be on the applicant to prove that the prior art product or process differs with respect to the parameter.

While clarity is not generally a ground of opposition, if a parameter is not clearly defined, for example because a measurement method is missing, then uncertainty around the parameter value may broaden the scope of the claim. In some circumstances a poorly defined parameter may not be limiting at all. In both cases, this could lead to new prior art becoming relevant and vulnerability to novelty or inventive step attacks.   


Sufficiency can also be a potential problem when using parameters to define a product or process. Sufficiency is a ground of opposition before the EPO while clarity is not (except for in certain specific circumstances relating to post-grant amendments). This means that while a patent claim including a parameter cannot generally be attacked at opposition for lacking clarity, it could be attacked for not being sufficiently disclosed.

If a claim relates to a product, for example a composition, which is defined in part by a parameter, for example bioavailability, then it must be possible, based on the patent specification and the common general knowledge, for the skilled person to be able to make the compositions which exhibit the claimed bioavailability without undue burden.

In the case of ill-defined or ambiguous parameters or specifications lacking a measurement method for the parameter, the EPO will take a case by case and fact specific approach when considering sufficiency. An ill-defined or ambiguous parameter may not necessarily be enough in itself for a claim to lack sufficiency. Similarly, variation in the value of a parameter depending on the measurement method used does not necessarily lead to a sufficiency objection before the EPO.

While the EPO’s approach to assessing sufficiency of claims including parameters is less clear cut than for clarity, applicants can guard against sufficiency issues pre and post grant by ensuring that the parameter is clearly and precisely defined and that the specification includes a clearly described measurement method including the measurement conditions.


Parameters are an important tool for defining certain types of product or process, particularly in the chemistry and materials science fields. While there are many potential pitfalls which can be difficult to overcome after a patent application has been filed, these pitfalls can be avoided by careful drafting of patent specifications. If you would like to discuss ways in which to protect your inventions or you have a question on the use of parameters, then please contact Zack Mummery.

This article is for general information only. Its content is not a statement of the law on any subject and does not constitute advice. Please contact Reddie & Grose LLP for advice before taking any action in reliance on it.

[1] (EPO Guidelines F-IV, 4.11)

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