MV = PQ , where M is the supply of money, V is the velocity of money (the number of times per year the average dollar is spent on final goods and services), P is the price level (average price at which each unit of physical output is sold), and Q is the physical volume of goods and services produced. The left side is the total amount spent; the right side is total amount received. Monetarists believe that V is stable, or that the factors altering velocity change gradually and predictably.