AdWordsAdvisor2: How Currencies Are Converted

This was previously a secret:

"For competitive reasons, our AdWords product team does not want to release the source of our currency conversion calculations."

Now, in response to questions at WMW, AdWordsAdvisor2 says:

"To convert currencies for ad ranking, we receive a daily feed from Citibank and use the average of the buy and sell prices to determine the exchange rate."