Switching to a quantity of money target to get out from having to defend the high interest rates necessary to tighten money, Volcker allowed the federal funds rate to reach 20 percent for much of 1981.

FORBES: Reagan's Monetary History

Even Friedman before he died seemed to adjust his thinking on using the quantity of money as a target.

WSJ: Seth Lipsky: The Gold Standard Goes Mainstream

This is precisely the reason why most central banks target the price of money, in the form of short-term interest rates, rather than its quantity.

ECONOMIST: The unstoppable, surging yen