China’s President Hu Jintau arrives in Washington today for a state visit, turning the spotlight once again on U.S.-China trade and China’s allegedly undervalued currency, the yuan. Not one to let such an opportunity go to waste, Sen. Charles Schumer (D-N.Y.) is introducing legislation that would threaten to impose duties on imports from China if the yuan does not appreciate quickly.

Count me skeptical that a more expensive yuan relative to the U.S. dollar would make much of a dent in our bilateral trade deficit with China, or that it would have any positive effect on U.S. economic growth and employment. But even if those assumptions were true, the big story is how much the yuan as already appreciated against the dollar.

It has been a mantra of Sen. Schumer and other critics of U.S.-China trade that the yuan is undervalued by 15 to 40 percent. They were saying that before the 2005 appreciation, and they’re saying that now, as though nothing has changed.

Yet a lot has changed. In nominal terms, the yuan appreciated by more than 20 percent between 2005 and 2008. That’s when China relaxed its hard peg with the dollar and allowed its currency to gradually appreciate. After holding the peg steady again during the recent financial turmoil, China has again allowed it to rise another 3 percent since last June.

The nominal rate is just part of the story, however. Price levels in the United States and China determine the real exchange rate–the actual amount of goods that can be bought with each currency. A big story in China recently is its rising inflation rate, which makes Chinese goods relatively more expensive at any given exchange rate. In this way, a relatively higher inflation rate in China compared to the United States acts in the same was as a nominal increase in the exchange rate of the yuan.

When you combine the effect of rising prices in China with the higher nominal value of the yuan, you get a double boost to the real exchange rate. According to a chart on the front page of this morning’s Wall Street Journal, the real value of the yuan has appreciated by 50 percent since the beginning of 2005. In early 2005, 100 Chinese yuan could be exchanged for about $12; today it can be exchanged for $18 (in real, inflation adjusted dollars).

Rather than complain, Sen. Schumer and his allies should congratulate themselves on achieving their goal of a much stronger yuan and a much weaker dollar, even if we are still waiting for the tonic effect they predicted it would have on jobs and growth.