Patent infringement: Improver question of ‘material variation’ unnecessary and unhelpful

Patent infringement: Improver question of ‘material variation’ unnecessary and unhelpful

Australian Mud Company Pty Ltd v Coretell Pty Ltd [2010] FCA 1169

This Australian Federal Court decision states it is neither necessary nor helpful to use the Improver question to consider whether a variation of an invention (e.g. replacement of a single-part device by two separate parts) is ‘material’ so as to avoid infringing a patent in circumstances where, on a proper purposive construction of the wording of the claims, the monopoly claimed does not include the variation.


Australian Mud Company sued Coretell for infringement of an innovation patent concerned with drill core orientation tools used in the mining industry. Coretell denied infringement, and cross claimed for invalidity.

The decision

Claim construction

The claims of the innovation patent referred to “An orientation device”. Coretell’s orientation tool had two parts. The rival contentions of the parties as to the meaning of the word “device” were as follows:

(a) Coretell said the word “device” literally meant a single part.
(b) Australian Mud Company said the word should be construed purposively using the Improver question to find that replacement of a single part by two parts was not a ‘material variation’ that avoided infringement.

The Improver question1 has the following three parts

  1. Does the variant have a material effect upon the way the invention works? If yes, the variant falls outside the claim. If no:-
  2. Would this fact (i.e., that the variant has no material effect) have been obvious to the skilled person at the date of publication of the patent? If no, the variant falls outside the claim. If yes:-
  3. Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention? If yes, the variant is outside the claim. If no, then the variant falls within the scope of the claim.

Coretell’s two-part tool would not be a ‘material variation’ that avoided infringement if the three parts of the Improver question were answered as follows – (1) the change from one part to two parts had no material effect on the way the invention worked; (2) it would have been obvious to an expert that two parts would work in the same way; and (3) the skilled reader would have understood from the patent that the patentee had not meant to confine his claim to a “device” in its primary meaning but in a wide generic sense.

The Court rejected both strict literalism and being shoehorned into using the Improver question of ‘material variation’ as a proxy for purposive construction. Instead, His Honour conventionally used the principle of purposive construction to reconcile the literal meaning of the word “device” with the context provided by the rest of the specification.

Purposive construction

His Honour found that, on a proper purposive construction, the “device” of the claims must be a single part, not two separate parts because the specification as a whole never suggested at any point that the invention encompassed tools in more than one part. Conversely, one dependent claim referred to “an orientation device as claimed in claim 1” which is “attached to an inner tube assembly of a core drill”. This clearly inferred that the device was a unitary device the whole of which attached to the core drill. The dependent claims also referred to “the orientation of the device” which suggested a whole device, i.e., one in a single part.


The result of the proper purposive construction was that Coretell did not infringe because its two-part tool was not within the scope of the word “device” as used in the claims.

Improver question of ‘material variation’

Having found there was no infringement using purposive construction, His Honour said there was no need to go into the Improver question, stating that:

“the question of “material variation” is not a useful means of determining whether or not there has been an infringement of the Patent. Rather, the particular question is the proper construction of the claims. Once it is determined that the invention described in the Patent does not include a two part device, then no question of material variation arises”.2


This case is a good reminder that the Improver question of ‘material variation’ is not a substitute for purposive construction.


  1. Improver Corporation v Remington Consumer Products Ltd [1990] FSR 181
  2. At [107].