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A parametric claim is one that defines a product or feature of a process in terms of its parameters, for example:

‘A composition comprising a detergent having an XYZ value of greater than 5.0.’

This style of claiming is referred to as ‘parameteritis’ or ‘parametritis’ and was discussed by Laddie J in Raychem Corp.’s Patents [1998] RPC 31 at page 37:

"This is the practice of seeking to repatent the prior art by limiting claims by reference to a series of parameters which were not mentioned in the prior art.  Sometimes it includes reference to a series of parameters measured on test equipment which did not exist at the time of the prior art.  The attraction of this to a patentee is that it may be impossible to prove now that the prior art inevitably exhibited the parameters and therefore it is impossible for an opponent to prove anticipation.  Even if that is what has happened here, it does not alter the task of the court.  It must decide whether the opponent has proved anticipation or some other statutory ground of invalidity.  Parametritis may make the court’s task more difficult, but at the end of the day the test of invalidity must be the same, whatever the form of the claims."

At pages 46-47, Laddie J stated in relation to the parameter S/D volume ratio:

‘It is essentially arbitrary and has little technical significance.  The selection of a group of compositions by reference to such a parameter does not involve any inventive step.  Although it may not be obvious, in the common use of that word, to limit a claim by reference to this particular meaningless and arbitrary parameter, that has nothing to do with patentability.  Patents are not given for skill in inventing technically meaningless parameters.’

Examination Practice

A parametric claim is not objectionable merely because it defines a product in terms of its parameters.  The defining of a product by its parameters may be appropriate where the product cannot be adequately defined by other means.  However, the parameters must be clearly and reliably determined, either by objective procedures known in the art or as indicated in the description.  Similar considerations apply to a feature of a process that is defined in terms of its parameters.

As noted in Euroceltique S. A. [2009] APO 21 at [112], a key consideration when construing parametric claims is whether the parameters are chosen to achieve a technical effect, or whether they are an arbitrary convenience.  Where a claim defines a new or unusual parameter that is not recognised in the art, a clarity objection may be appropriate.

Novelty Considerations

Examiners should be aware that the use of parameters within a claim may be an attempt to disguise a lack of novelty.  In Williams Advanced Materials, Inc. v Target Technology Company LLC [2004] FCA 1405 the claims under consideration were directed to an optical storage medium comprising a silver and palladium metal alloy.  At paragraph 48 Bennett J stated:

“Indeed, there is nothing in the specification that suggests that the proportions or the ranges of metals in the alloys are in any way part of the invention, other than the mere reference to them.  It is a case of ‘parameteritis’.”

Certain claims were found to be not novel.

However, in Austal Ships Pty Ltd v Stena Rederi Aktiebolag [2005] FCA 805, claims directed to a hull with certain parameters were found to be novel.  In this case Bennett J stated at paragraph 108:

"Unlike in Williams Advanced Materials, Inc. v Target Technology Company LLC [2004] FCA 1405 at [48], there is reference in the patent specification and evidence which supports the fact that the parameters have been carefully chosen, are part of the invention and are related to a claimed advantage as part of the combination of the design."

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