Rectification of mistakes permits tax authorities to amend orders subject to notice, hearing and statutory time limits. Section 35 empowers specified wealth tax authorities, including the Assessing Officer, Valuation Officer, appellate and revisional authorities and the Tribunal, to amend their own orders to rectify mistakes apparent from the record. Amendments that enhance liability or reduce refunds require prior notice and an opportunity to be heard, must be made by written order, and where liability increases a prescribed demand notice is to be issued. Time limits apply, generally barring amendments after four years, with a limited one year window for consequential valuation-based assessment changes.