Adding Currency Conversion - Expert Cube Development with SSAS Multidimensional Models - page 192

At this point, the wizard shows a new page, Define Local Currency Reference ,
where we tell the wizard how to determine the Local Currency used in each
transaction. In the examples we are using, we have to select the Currency
attribute of the Currency dimension.
Alternatively, it is possible to use an attribute of another dimension to store the Local
Currency. This would be the case, for example, if the currency to use was stored in
an attribute related to a Country attribute on the Customer dimension.
It is very unlikely you'll have a source data mart where measures
are stored in a Local Currency, but where you don't know what that
currency is. This is only likely to happen in prototypes of cubes based on
raw data imported from several sources without any ETL in the middle.