How currency affects budgets
When you define or maintain budgets, you can specify a budget currency. For activity group budgets, you must use the base currency. For activity budgets, you can select any currency associated with the activity group's currency table. However, to ensure the ability to perform budget to actual comparisons at all activity levels, it is recommended that you define activity budgets using base or report currencies.
Exchange rates for budget currencies are stored in the activity budget header record. Exchange rates are used to convert the budget currency to base currency and report currencies. The currency exchange rates in effect at the time the budget is defined are used by default, but you can enter different rates if desired.
You can update the exchange rates in budget header records if you haven't added the budget detail records yet, but you need to copy budgets before modifying exchange rates. This lets you preserve multiple budget iterations, each with the exchange rate in effect at the time the budget was created.