The income years over which you must average your * basic taxable income are:
(a) if this Division has applied to your assessment for at least 4 income years in a row (including the * current year)--the current year and the 4 previous income years; or
(b) if this Division has applied to your assessment for less than 4 income years in a row (including the * current year)--those income years and the last income year before them.
Note: You may need to average your basic taxable income for one or more income years before the 1998 - 99 income year. See section 392 - 1 of the Income Tax (Transitional Provisions) Act 1997 .