often compare the performance of the S&P 500 in USD with the performance of the Nikkei 225 in JPY, i.e. the return for an American and a Japanese investor who invest in their respective home market. I comparerd the return of a European investor who invests unhedged (currency) in the U.S to the return of a Japanese investor who invests at home. [Shortcoming: I didn't take dividends into account. Bloomberg offers a total return index for the S&P 500 going back to 1988. I have no clue how much dividends Japanese companies pay.]

The chart is fun to look at, but I don't know how useful it is (Deflation in Japan). The US-Dollar lost 70% against the Yen since 1975 (from 300 to 95) and "EURUSD" (Euro, Ecu, EUA) stayed flat over that period. So the Euro lost as much. A chart of the Nikkei in EUR would look pretty different.