Exemption from customs duty on low-ash coking coal limits duty to 5% ad valorem and waives additional duty. Imported coking coal of ash content below 12% falling under Chapter 27 is exempted from customs duty in excess of an amount calculated at 5% ad valorem and from the whole of the additional duty levied under the Customs Tariff Act, the exemption being granted by the Central Government under statutory power in the public interest.