Customs effective rates cap additional import duty by exempting duty beyond prescribed rates for listed tariff items. The notification exempts imported goods specified by chapter, heading, sub heading or tariff item from customs duty to the extent that such duty exceeds the amount calculated at the prescribed standard rate or, where applicable, the prescribed preferential rate in the table; the table rates are ad valorem unless a specific duty alternative is stated, and certain entries provide a specific duty floor or special effective rate.