Exemption on medical X ray films: excise duty limited to an ad valorem cap, excess duty exempted under Central Excise Rules. The Central Government exempts medical X ray films under sub headings 3701.10 or 3702.10 from that portion of excise duty exceeding the amount computed at an ad valorem cap of five per cent, using powers under rule 8(1) of the Central Excise Rules, 1944, thereby capping effective duty payable on those tariff items.