Customs exemption for kerosene used in N paraffin extraction requires certified monthly reporting and duty adjustment. Exemption allows reduced customs duty on kerosene imported by manufacturers of linear alkyl benzene for extraction of N-paraffin, with full exemption for kerosene remaining after extraction and supplied to Indian Oil Corporation. Importers pay duty on 85% of imports at importation, maintain certified monthly accounts of consumption and sales, and submit statements to the Excise officer. The Excise officer, exercising Customs assessing powers, determines consumed and sold quantities, adjusts duty paid, orders additional duty or refunds, and mandates payment within three days with interest on delayed payments.