A Ratio Forward is a foreign exchange contract, which protects you against the risk that the exchange rate is unfavourable to you when compared against a nominated worst-case rate (WCR). It also allows you to benefit from a favourable move in the exchange rate in relation to an agreed proportion of the face value of your contract.
If the spot exchange rate is more favourable to you than the WCR at the expiry time on the expiry date then, you must settle an agreed proportion of the face value at the WCR and the balance can be settled at the more favourable spot exchange rate.
If the spot exchange rate is less favourable to you than the WCR at the expiry date, you are protected at the WCR for the face value.