the first two letters of the code are the two letters of iso 3166-1 alpha-2 country codes (which are also used as the basis for national top-level domains on the internet). the third letter is usually the initial of the currency itself. so japan's currency code is jpy, "jp" for japan and "y" for yen. this eliminates the problem caused by the names "dollar, franc" and "pound" being used in dozens of different countries, each having significantly differing values. also, if a currency is revalued, the currency code's last letter is changed to distinguish it from the old currency. in some cases, the third letter is the initial for "new" in that country's language, to distinguish it from an older currency that was revalued; the code sometimes outlasts the usage of the term "new" itself (for example, the code for the mexican peso is mxn). other changes can be seen, however; the russian ruble, for example, changed from rur to rub, where the b comes from the third letter in the word "ruble".