Average adjusted total Income definition guides computation under section 44C based on the number of prior assessment years. The definition of Average adjusted total Income prescribes computation by averaging the assessee's adjusted total income from prior assessment years: one-third of the aggregate when assessable in each of the three immediately preceding years; one-half of the aggregate when assessable in only two of those years; and, where assessable in only one of those years, the amount equals the adjusted total income for that single prior year.