The underground economy and other nonpriced production make it hard to accurately measure the precise level of GDP. But GDP could still be very accurate for measuring changes in the economy. If Ben Bernanke, the Federal Reserve chairman, is trying to find out whether the U.S. economy has gone into a recession, are the difficulties of measuring nonpriced production likely to be important problems for his purposes? How is this like always wearing your shoes when you step on the bathroom scale?