Excise exemption limits duty on Computer Numerical Control systems to a specified ad valorem effective rate. The Central Government exempts Computer Numerical Control systems under Chapter 85 from excise duty in excess of the amount calculated at a 5 per cent ad valorem rate, under sub rule (1) of rule 8 of the Central Excise Rules, 1944 by Notification No. 87/88 C.E. dated 1 3 1988, fixing the effective rate of duty at that ad valorem percentage.