...
The Settlement Currency field only affects the specific trade, not the underlying security. Suppose you change the Settlement Currency field to CAD. The system unlocks the Settlement Net Amount field, allowing you to enter a settlement amount. This is the local CAD amount in the example that follows.
When the trade settles, the cash is settled in Canadian dollars, as specified on the trade panel.
NOTE: You must have a CAD-to-USD FX rate available for the specific FX Source for the entity for the system to settle the non-base transaction. The system uses the most recent rate (by source) from the settlement date of the trade.
...