Customs duty exemption limits excess basic duty on Chapter 1 imports to a prescribed ad valorem rate. The government, exercising power under section 25(1) of the Customs Act, 1962, exempts goods under tariff headings 01.01-01.06 from that portion of basic customs duty in the First Schedule which exceeds the ad valorem rate specified in the Table, thereby capping the effective basic duty payable on those imported goods.