 Since the money supply consists of various financial instruments (usually currency, demand deposits and various other types of deposits), the amount of money in an economy is measured by adding together these financial instruments creating a "monetary aggregate".Modern monetary theory distinguishes among different ways to measure the stock of money or money supply, reflected in different types of monetary aggregates, using a categorization system that focuses on the liquidity of the financial instrument used as money.The most commonly used monetary aggregates (or types of money) are conventionally designated M1, M2 and M3.