Unusual parameters are parameters not commonly used in the field of the invention. Two main situations can present themselves:
The unusual parameter measures a property of the product/process for which another generally recognised parameter is used in the field of the invention.
The unusual parameter measures a property of the product/process that was not measured before in the field of the invention.
In addition to the requirements contained in F‑IV, 4.11:
Cases in which an unusual parameter of type (i) is employed and no straightforward conversion from the unusual parameter to the parameter generally recognised in the art is possible, or a non-accessible apparatus for measuring the unusual parameter is used are prima facie
objectionable on grounds of lack of clarity, as no meaningful comparison with the prior art can be made. Such cases might also disguise lack of novelty (see G‑VI, 6
Use of unusual parameters of type (ii) is allowable if it is evident from the application that the skilled person would face no difficulty in carrying out the presented tests and would thereby be able to establish the exact meaning of the parameter and to make a meaningful comparison with the prior art. In addition, the onus of proof that an unusual parameter is a genuine distinctive feature vis-à-vis the prior art lies with the applicant. No benefit of doubt can be accorded in this respect (see G‑VI, 6
Example of an allowable unusual parameter of type (ii)
The application explains that the abrasive action of sandpaper of very fine grade is improved if strips with abrasive grain are alternated with strips without abrasive grain. Claim 1 contains an unusual parameter of type (ii) that measures the relationship between the widths of the abrasive strips and the non-abrasive strips within a certain length of the sandpaper.
The skilled person has no problem in establishing the exact meaning of the parameter, measuring it and determining its genuine distinctive feature against the prior art.