Patent & Trade Mark

Not all errors are obvious

Date: 13 November 2009
Author: Jacqueline Warner

BHP Billiton SSM Development Pty Ltd v Cominco: Engineering Services (2009) APO 10 (11 June 2009)

Key Points:

  • Claims of an accepted application may be broadened in scope following amendment only if the amendment is for the purpose of correcting i) "a clerical error" or ii) an "obvious mistake"
  • In order to avoid the refusal of an amendment, it is critically important to decide whether the amendment sought is the result of a clerical error or is an obvious mistake
  • This case highlights how the reason for the correction is not always easily identified and that a careful consideration of the facts is required.

Note: Terminology

Clerical Error: an error that has arisen in the mechanical process of writing or transcribing

Obvious Mistake: the existence of a mistake is obvious and the correction required is also obvious.


This case was a decision of a Delegate of the Commissioner of Patents and concerned the allowability of amendments made to the claims of an accepted patent application.

Patent Application No. 740712 in the name of Cominco Engineering Services was accepted and the grant of the patent was subsequently opposed.  During the opposition proceedings, Cominco filed a number of amendments to the claims and description which were opposed by BHP Billiton SSM Development Pty Ltd.

The major consideration by the Delegate concerned the allowability of an amendment to claim 1, in which the expression "the resultant pressure oxidation slurry" was replaced with "the resultant acid leaching slurry", as indicated below:

     "A process for the extraction of metal from an ore or concentrate, containing nickel and/or cobalt values and other metals, comprising the steps of:

     subjecting the ore or concentrate to acid leaching under pressure, at pH<2, to obtain a liquor at pH<2 containing nickel and/or cobalt values in addition to non-nickel and non-cobalt metals from the resultant pressure oxidation acid leaching slurry;....."

Cominco indicated that the amendment was to correct an obvious error as there was no antecedent for "pressure oxidation" in the claim.  BHP alleged that the amendment constituted claim broadening.

Australian law

An amendment of an accepted specification is generally not allowable if the amendment results in a claim that falls outside the scope of the claim before amendment.  An exception to this rule exists where the amendment has been made for the purpose of correcting a clerical error or an obvious mistake made in, or in relation to, a complete specification.  Evidence to support such a request for amendment is usually required.

Scope of claim 1 before and after amendment

Before amendment, claim 1 specified that the acid leaching of the ore was carried out oxidatively.  The Delegate concluded that the amendment to claim 1 would remove the oxidation requirement, so that it would not in substance fall within the scope of the claim before amendment.

The amendment, therefore, would only be allowable for the purpose of correcting a clerical error or obvious mistake.

Was there a clerical error or an obvious mistake?

The evidence provided by Cominco to support the amendment included statutory declarations from Mr Jansen and the draftsman, Mr de Kock.

Arguments for Obvious Mistake

The key features of an obvious mistake are that the mistake must be obvious and the correction must also be obvious.

Cominco argued that it was obvious that the use of oxidation was an error because the claim included laterite ores, which did not require oxidation.  Jansen supported this by stating that "it does not make sense to apply a pressure oxidation leach to a laterite ore because the ore is already oxidised".  Jansen further stated that the inclusion of the expression "resultant pressure oxidation slurry" was an obvious mistake and not a clerical error and that the error was a careless drafting error.

The Delegate noted that while oxidation leaching was not necessary in the case of laterite ores, the evidence established that there were situations where oxidation leaching of laterites could be considered appropriate and therefore while unusual, was not an absurd construction of the claim.

The Delegate also conceded that there was an inconsistency between the description and the claims, as the claims included treatment of laterite ores by oxidative leaching which was not taught by the description.  He concluded, however, that even if the presence of the mistake was obvious he was not satisfied that the correction was obvious.

It was argued by Cominco that the obvious correction was to delete the requirement of oxidation.  However, if this were done the claim would include the leaching of sulphide ores under non-oxidative conditions which was inconsistent with the teaching of the art and specification.  Further, the Delegate noted that it seemed equally possible that that the correction of the claim could be the exclusion of laterite ores from the claim.  The correction proposed by Cominco, therefore, was not obvious.

The Delegate concluded that where the alleged correction introduced new deficiencies into the claim, e.g. a new inconsistency, that is an indication that the correction was not obvious.  Also the presence of alternative corrections indicated that the correction was not obvious.

Arguments for Clerical Error

The characteristics of a clerical error is not that it is in itself trivial or unimportant, but that it arises in the mechanical process of writing or transcribing.  A clerical error arises where a person either of his own volition or under the instructions of others intends to write something and by inadvertence either omits to write it or writes something different.

The statutory declaration of de Kock, revealed that he was the draftsman for the priority application and the corresponding PCT application.  In preparing the PCT specification, he was instructed to prepare claim 1 covering both sulphide and laterite ores, referring only to acid leaching and not oxidation leaching.  Due to inadvertence, he did not give effect to the instruction because he failed to amend a portion of the template document that he was using.  His declaration was accompanied with a copy of the original work piece showing his changes in longhand confirming that he overlooked changing "resultant pressure oxidation slurry" to "resultant acid leaching slurry".  It was clear that an error was made in the process of drafting the PCT specification.

The Delegate was satisfied that the amendment to claim 1 was for the purpose of correcting a clerical error.


In this case, the declaratory evidence of one of Cominco's declarants, Jansen, was in conflict with that of another of their declarants, de Kock.  For this reason the Delegate could have refused the amendment but instead he gave preference to the evidence of de Kock on the basis that he was a person having first hand knowledge of the facts and had provided those facts rather than an unsupported opinion.

This case demonstrates that the distinction between a "clerical error" and an "obvious mistake" is not always clear.  Where an amendment results in claim broadening and "clerical error" or "obvious mistake" is to be relied upon, it is important to examine all the facts surrounding the reason for making the amendment so that the purpose of the correction can be correctly decided before the amendment is filed.  This case also suggests that an "obvious mistake" is difficult to establish.  If a mistake appears obvious but there is more than one alternative to correct it, then "obvious mistake" is not applicable.  A "clerical error", on the other hand, may be more easily established because it is based on fact which can be provided by someone who has first hand knowledge of the facts.

Tags:  Clerical error, obvious mistakes
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