Rectification of mistakes: officer may amend orders within two years, with notice and hearing if liability is increased. The Central Excise officer who passed an order may rectify mistakes apparent from records within two years, on his own motion or when brought to notice by the assessee, the Commissioner or Commissioner (Appeals); rectification must be by written order. Matters decided in appeal or revision cannot be rectified, though other portions not so adjudicated may be amended. Amendments that enhance liability or reduce refunds require notice and a reasonable opportunity to be heard, and the officer must specify sums payable; amendments reducing liability require payment of any refund due.