Because of all the reasons why the law of one price does not literally hold, economists certainly do not expect this equation to give an exact prediction of the exchange rate. Nevertheless, it can provide a useful indication of whether a currency is undervalued or overvalued. A currency is undervalued if, following this equation, its price is too low compared to the ratio of price levels in the two countries. A currency is overvalued if, following this equation, its price is too high compared to the ratio of price levels in the two countries. As in our discussion of the euro, if a currency is overvalued, then we would expect its value to decrease over time. This is called a depreciation of the currency. Likewise, we would expect the price of an undervalued currency to increase over time. This is called an appreciation of the currency. The market forces behind these currency movements come from the buying and selling of currencies for trading purposes. If the Chinese yuan is undervalued, goods produced in China will be relatively cheap in US dollars. The demand for Chinese exports will be high, and this will lead to a large demand for the yuan. Eventually the dollar price of the yuan will increase— that is, the yuan will appreciate, and the dollar will depreciate. Changes in the Exchange Rate Even though the law of one price does not literally hold for all goods and services, it reminds us that the value of $1 in the United States is linked to its value in the rest of the world. As a result, we expect that price level changes are likely to lead to changes in the exchange rate. We see this more clearly if we write our previous equation in terms of growth rates. Using the formula for growth rates, we find the following: growth rate of price of dollar in euros = growth rate of price of European bundle of goods− growth rate of price of US bundle of goods. Toolkit: The formulas for using growth rates can be found in the toolkit. If the bundle of goods in each country corresponds roughly to the goods in the Consumer Price Index (CPI), then the growth rate of these prices corresponds to the inflation rate. The growth rate of the exchange rate is just another term for the percentage appreciation of the currency. Thus we get the following: percentage appreciation of the dollar ≈ European inflation rate − US inflation rate. So, if the inflation rate in the United States is higher than it is in Europe, we expect the euro price of the dollar to decrease. We expect depreciation of the dollar if US inflation exceeds European inflation. Inflation reduces the real value of money domestically; it will also tend to reduce the value of money in terms of what it can purchase in the rest of the world. This makes sense. If our currency is becoming less valuable at home, then we should also expect it to become less valuable in the rest of the world. The Real Exchange Rate The law of one price is connected to another measure of the exchange rate—the real exchange rate. This exchange rate is a measure of the price of goods and services in one country relative to another when prices are expressed in a common currency. It is about exchanging goods, rather than money, across countries.