Where one or other of the situations described in pars (a), (b) and (c) of s. 167 exists, the Commissioner or his delegate is empowered to make an assessment of an amount which, in the Commissioner's judgment, is the amount on which tax ought to be levied: George's Case [10] . It is that amount which, for the purpose of s. 166, becomes the taxpayer's taxable income. That amount may not be in truth the taxpayer's taxable income for a particular income year and it may not be so regarded by the Commissioner (as in Trautwein v. Federal Commissioner of Taxation [11] ) but, for the purpose of s. 166, that amount is the taxpayer's taxable income for the income year to which the assessment relates unless it is shown on appeal from, or on review of, the assessment that the amount of the assessment is wrong: Henderson v. Federal Commissioner of Taxation [12] . In a case arising under s. 167(b), there are two functions for the Commissioner or his delegate to perform: first, he must decide whether he is satisfied with the return furnished, and, if he is not, he must form a judgment of the amount on which tax ought to be levied. In George's Case [13] it was held that the former function was a procedural step and was thus part of the making of the assessment, the due making of which is conclusively proved by the production of a notice of assessment: s. 177(1). By contrast, in proceedings on appeal against an assessment the function of forming a judgment of the amount on which tax ought to be levied is not conclusively proved by the production of a notice of assessment. That is because s. 177 distinguishes "between the procedure or mechanism by which the taxable income and tax is ascertained or assessed on the one hand and on the other hand the substantive liability of the taxpayer. The former involves the due making of the assessment": George's Case [13] ; McAndrew v. Federal Commissioner of Taxation [14] ; and see F.J. Bloemen Pty. Ltd. v. Federal Commissioner of Taxation [15] .