Best judgment assessment: AO issues show cause notice, affords hearing, then determines taxpayer's income to best judgment. Best judgment assessment under section 144 requires the Assessing Officer to serve a show cause notice when circumstances justify such assessment, consider all relevant material, and, if not satisfied by the taxpayer's responses, after affording an opportunity of being heard, determine total income or loss and the sum payable to the best of his judgment; no separate show cause notice is required if a notice under section 142(1) was earlier issued.