The Crowd Fundraiser plugin allows Campaigns to be conducted in any of the currencies supported by Seamless Donations (which in turn are the currencies support by PayPal). When a donor makes a donation in a currency other than that of the cause/campaign, the website needs to convert the amount of the donation in order to determine funding levels. This is only an approximate conversion since the actual conversion is done by PayPal or the bank handling the money transfer. To get exchange rates, the Crowd Fundraiser plugin uses the WP Currency plugin which in turn pulls currency data from openexchangerate.org. To setup WP Currency, you need an API key (free from openexchangerates.org) and an update interval. Since exchange rates rarely have large moves, an update interval of daily is fine for purposes of estimating funding.