Since the early 1960s, the level and the rate of growth of potential output have become increasingly important subjects. While policymakers’ and the public’s acceptance of these concepts has become widespread, since the early 1970s there has been considerable controversy concerning the measurement of potential output and its growth. By 1973 it had become clear to many observers that the Council of Economic Advisers’ (CEA) measure of potential output was too high. That measure showed slack in the economy equal to $30 billion (1972 dollars) while many observers thought the economy was operating at or above its potential, at least in the early part of the year.