Block assessment procedure requires a prescribed notice and return of undisclosed income, with limited revision and prescribed approvals. Special procedure for block assessment requires the Assessing Officer to issue a prescribed notice after a search or requisition, demanding a verified return of undisclosed income for the block period within the specified period; late returns are not regular returns, revision is barred, and a conditional thirty-day extension for audit may be granted. The Assessing Officer must determine total undisclosed income per the separate valuation mechanism, apply listed assessment and penalty provisions as applicable, pass an assessment or reassessment to compute tax, and ensure seized or requisitioned assets are dealt with under the asset-handling rule, with prior approval required before issuing the notice.