Power of survey enables tax authorities to enter premises to inspect books, verify stock, and require information. Section 133A authorises specified income-tax authorities to enter business or related premises during prescribed hours to inspect books of account and documents, verify or check cash, stock and other valuable articles, and require information; it permits marking records, making extracts, impounding documents subject to recorded reasons and supervisory approval, making inventories and recording statements, prohibits removal of cash or stock from the premises, and provides enforcement by invoking powers under section 131 where compliance is refused.