Occasionally, exporters may approach Authorised dealers for reduction in invoice value on account of cash discount to overseas buyers for pre-payment of usance bills. In such cases authorised dealers may agree to the exporter granting cash discount to the overseas buyer to the extent of amount of proportionate interest on the unexpired period of usance calculated at the rate of interest stipulated in the export contract or at the prime rate of the currency of invoice where rate of interest is not stipulated in the contract.