Sage 200 can hold the details of up to 100 currencies. One is your base currency. The remaining are the currencies in which your customers and suppliers operate.
You can use single and period exchange rates for each currency. Period exchange rates allow you to set your exchange rates with date ranges. You must have chosen Use period exchange rates in the Accounting System Manager settings Operations tab.
When entering transactions in a foreign currency:
The exchange rate is used to calculate the value of your foreign currency into your base currency.
This exchange rate is taken from the exchange rate table which you set up using the Currencies and Exchange Rates option in Accounting System Manager > Settings. If the exchange rate is amendable, you can change it when entering transactions.