Your "default" currency will be reflected in several areas of the Trade > Overview page:

• "Total" value in the Balances table
• Trade Balances section
• Position Valuation section

The currency used for these values is based on the currency pair that you have selected in the left-side of the black bar on the top of the page and the setting is saved in your browser cookies. 

Note: the 30-day trade volume counter (aka the "blue bar"), is always in USD.

Example of USD "default" currency.

Example of EUR "default" currency.