Mahenthirarasa v State Rail Authority & Ors  NSWCA 101. Basten JA, Bell JA agreeing, Giles JA shortly separately.
Basten JA, to the statute, at :
"The concept of 'demonstrable error' is not defined, and may be open to various interpretations, ranging from the broad to the narrow. At the narrowest end of the spectrum, it may be thought that the error must be apparent from reading the certificate itself, thus equating the error with error 'on the face of the record' for the unrelated purpose of relief in the nature of certiorari. There is no obvious reason why such a construction should be adopted when the purpose is review on the merits, rather than review for legal error. The word 'demonstrable' does not in any event import such a constraint. As noted at  above, the example given in the second reading speech suggested that the error must be a manifest error."
Basten JA quoted Gleeson CJ in Plaintiff S157/2002 v The Cth  HCA 2; 211 CLR 476 at .
Then, "In Merza v Registrar WCC  NSWSC 939, Hoeben J thought it was sufficient that an error is one 'readily apparent from an examination of the medical assessment certificate'. That is also sufficient for the present case, although it may not constitute a necessary element of the statutory formulation. The matter was considered further in the recent decision of this Court in Pitsonis v Registrar WCC  NSWCA 88 ' in the judgment of Mason P, with whom McColl and Bell JJA agreed.
"The appeal included a ground based on demonstrable error which was, on its face, valid and apparently credible. Its existence, in the absence of any clear basis for its rejection, should have led the primary judge to conclude that the delegate had failed to exercise his function according to law. In that respect his Honour erred and the appeal should be allowed."
Haroun v Rail Corporation NSW  NSWSC 160. Harrison AsJ.
19 A "demonstrable error" includes an error which is readily apparent from an examination of the medical assessment certificate and the document referring the matter to the AMS for assessment. It embraces something more than an "obvious error" which the registrar can correct.
"An error will be demonstrable if it is capable of being shown.
"Factual errors, particularly of a medical kind, or errors of logic or analysis if they are readily demonstrable from an examination of the medical assessment certificate, will amount to demonstrable error - see s 325(3), Merza v Registrar of the Workers Compensation Commission  NSWSC 939 at ; Pitsonis v Registrar of the Workers Compensation Commission  NSWSC 50 at ; and Smith v Liquip Services Pty Ltd  NSWSC 687.
Upheld on appeal: Haroun v Rail Corporation New South Wales & Ors  NSWCA 192 18.08.08.