Revision power allows Commissioner to correct orders prejudicial to revenue, subject to limitation and specified exceptions. The Commissioner may examine records of proceedings and, if an Assessing Officer's order is erroneous and prejudicial to revenue, after hearing the assessee and making enquiries, pass revisional orders including enhancement, modification, cancellation or fresh assessment; 'record' includes all material available at examination, the power covers matters not considered in appeal, and a two-year limitation applies subject to exclusions and exceptions for orders giving effect to higher forum findings and periods of rehearing or judicial stay.