NEW YORK — Stocks had another wild day, but there was no big event, no surprise announcement behind the swings.

All that happened was that the euro, battered to a four-year low yesterday before trading began in the U.S., started rising again. And the stock market followed the currency shared by 16 European nations.

Investors are looking at the euro as an indicator of confidence in the European economies. The euro has been sliding on concerns that debt problems will undermine Europe's recovery, and in turn that of the U.S. And so, when it started rising yesterday, stock traders interpreted its move as a "buy" sign.