If you select different currencies for your pipelines, the forecast and report will convert the values in other currencies to the default currency of your account.
The conversion is made at the most recent rate. This means that the converted values that you see in the report or forecast may vary from day to day, depending on the current currency rate.
The conversion rate source is currencylayer.com.
How to set the default currency
Navigate to the Settings > Account settings and scroll to the bottom of the page.
Only one currency can be selected as the default currency of the account.