If the banks have to keep no less than 10 percent of their deposits in the form of reserves, and then the Fed suddenly lowers that ratio to 5 percent, the nation's money supply, that is of bank deposits, will suddenly and very rapidly double. And vice versa if the minimum ratio were suddenly raised to 20 percent; the nation's money supply will be quickly cut in half. Ever since the Fed, after having expanded bank reserves in the 1930s, panicked at the inflationary potential and doubled the minimum reserve requirements to 20 percent in 1938, sending the economy into a tailspin of credit liquidation, the Fed has been very cautious about the degree of its changes in bank reserve requirements. The Fed, ever since that period, has changed bank reserve requirements fairly often, but in very small steps, by fractions of one percent.