Check Exchange Rate Types allow you to define different type of exchange rates in the system. This could be useful when it is necessary to define different exchange rates for the same period which will be used by different SAP Components.
IMG Path: SAP NetWeaver -> General Settings -> Currencies -> Check Exchange Rate Type
When you open the transaction, click on new entries if you want to create new exchange rate type otherwise maintain the already defined types.
After New Entries button you should maintain the exchange rate type with related options.