How to Tell Which Currency's Overvalued and Undervalued?

The dollar index, which compares its price against six key currencies with the highest weightings overwhelmingly for the euro, British pound and Japanese yen. Those have gotten clobbered, so it makes the dollar look like it's up a lot. The Federal Reserve instead watches a trade weighted index that puts more emphasis on the currencies of China, Mexico and Canada. And the US dollar isn't nearly as much relative to those.