Understanding the Transaction Currency Values
The SunSystems multi-currency/dual base currency functionality allows up to four different values to be held against every transaction throughout the SunSystems suite:

base currency value - value1 transaction currency value -  value 2 second base or reporting currency - value 3 memo value

One of the three currency values (1,2,3) is used as the basis for the currency conversions. This is called the pivot currency.
When you set up a business unit, you must choose the pivot value and determine the posting rules that control the use of the three currency values. You can determine which of the currency values are required, whether they must or must not be entered on each journal transaction, and whether they can be calculated by the system.
What is the Base Currency – value1?
The base currency is a single currency that is nominated for the business unit. This is typically the book accounting currency and is often the national currency of the country in which the company is based. Fiscal reporting is almost always carried out in this currency. For example, for a British company the base currency is probably GBP - sterling.
Every transaction in SunSystems contains a base currency value.
In a single currency environment, the base value is always entered on a journal transaction. In a multi-currency environment, the base currency value may be entered on a transaction, or calculated from either of the other currency values i.e. transaction currency or second base/reporting currency value.