Tax credit entitlement limited by supplier registration, invoice possession, and proportional usage with special capital goods rules. Tax credit is available only to registered dealers for input tax on purchases used for taxable sales or exports, subject to prescribed conditions and possession of tax invoice when filing returns. Exclusions include purchases from unregistered sellers, non-creditable goods, goods for incorporation into owner-occupied buildings (with resale/work-contract exceptions), purchases from certain dealers or casual traders, and where the seller has not deposited or lawfully adjusted tax. Capital goods and export-related removals attract phased credits, prescribed reductions, and reversals on sale or transfer within specified periods; the Commissioner may prescribe or reject apportionment methods.