The notification No. 20 1/79 prior to 1 Ith April, 1981 in so far as relevant for the present purpose was as follows: "Set off of duty on all exciseable goods on use of duty paid goods falling under Item 68 (Tariff Items I to 68): In exercise of the powers conferred by sub rule (1) of rule 8 of the Central Excise Rules, 1944, and in supersession of the notification of the Gov ernment of India in the Ministry of Finance (Department of Revenue) No. 178/77 Central Excise, dated the 18th June, 1977, the Central Government 271 hereby exempts all excisable goods (hereinaf ter referred as "the said goods"), on which the duty of excise is leviable and in the manufacture of which any goods falling under Item No. 68 of the first Schedule to the (1 of 1944) (hereinafter referred as "the inputs") have been used, from so much of the duty of excise leviable thereon as is equivalent to the duty of excise already paid on the inputs: Provided that the procedure set out in the Appendix to this notification is followed: Provided further that nothing contained in this notification shall apply to the said goods which were exempted from the whole of the duty of excise leviable thereon or are chargeable to nil rate of duty." The amending notification No. 102/81 dated 11th April, 1981 is as follows: "Provided also that credit of the duty allowed in respect of the inputs shall not be denied or varied on the ground that part of such inputs is contained in any waste, refuse or by product arising during the process of manufacture of the said goods, irrespective of the fact that such waste, refuse or by product is exempt from the whole of the duty of excise leviable thereon or is chargeable to nil rate of duty or is not mentioned in the declaration referred to in the Appendix to this notifica tion." Central Board of Excise & Customs issued Circular No. 6/81CX.