Customs duty exemption caps basic import duty for specified Chapter 6 goods to a declared ad valorem rate. The Central Government, under section 25(1) of the Customs Act, 1962, exempts imports of goods under specified Chapter 6 tariff headings from so much of the basic customs duty as exceeds the amount calculated at the declared ad valorem rate for each listed heading, thereby capping the basic duty payable on those goods at the stated ad valorem rate.