Exemption calculation method can be applied retrospectively when a later notification only clarifies how eligibility is determined.

A later excise notification that merely supplies a missing method of calculation may be used to determine eligibility under an earlier concessional notification, provided it does not expand the substantive scope of the exemption. On that reasoning, the average count of round mesh mosquito netting was held to be determinable even though the earlier notification did not prescribe a specific formula, and the calculation method in Notification No. 210/79-C.E. could be applied to the prior period. The concession was therefore available on the facts discussed.

---

---

Issues: Whether the average count of round mesh mosquito netting could be determined for the purpose of Notification No. 226/77-C.E. by applying the formula later prescribed by Notification No. 210/79-C.E., and whether the benefit of the concessional notification was available for the prior period.

Analysis: The earlier notification did not lay down a specific method for computing the average count of mosquito netting, but the absence of a detailed formula did not mean that the average count was incapable of determination. The later notification was treated as supplying the manner of calculation and not as enlarging the scope of the concession. On that basis, the same method could be used for the earlier period to ascertain the average count of the fabrics in question.

Conclusion: The average count of the mosquito netting was determinable, and the method prescribed by Notification No. 210/79-C.E. was able to the present matter for working out the average count. The assessee was entitled to the benefit of the concessional notification.

Ratio Decidendi: Where a later notification merely clarifies or supplies the method of calculation that was previously omitted, it may be applied to earlier cases to determine eligibility under the earlier concessional notification, provided it does not enlarge the substantive scope of the exemption.

---