As a medium of exchange, money permits the separation of exchange into the two distinct acts of buying and selling, without requiring the seller to purchase goods from the person who buys his products, or vice versa. Hence producers who know they will be paid in money, can concentrate on finding the most suitable outlet for their goods, while buyers who will pay in money, can concentrate on finding cheapest market for the things they wish to purchase. Specialization, which is vital to an advanced economy, is encouraged, because people whose output is not a complete product but only a part of one in which many others are involved can be paid an amount equivalent to their share of the product. Another advantage of money is that it is a measure of value, that is, it serves as a unit in terms of which the relative values of different products can be expressed. In a barter economy it would be necessary to determine how many plates were worth one hundred weight of cotton, or how many pens should be exchanged for a ton of coal, which would be a difficult and time-consuming task. The process of establishing relative values would have to be undertaken for every act of exchange, according to what products were being offered against one another, and according to the two parties'desires and preferences. If I am trying to barter fish bananas, for example, a lot would depend on whether the person willing to barter fish for bananas, for example, a lot would depend on whether the person willing to exchange bananas is or not keen on fish. Thirdly, money acts as a store of wealth. It is difficult to imagine saving under a barter system. No one engaged on only one stage in the manufacture of a person could save part of his output, since he would be producing nothing complete. Even when a person actually produced a complete product the difficulties would be overwhelming. Most products deteriorate fairly rapidly, either physically or in value, as a result of long storage even if storage were possible, the practice of storing products for years on would involve obvious disadvantages-imagine a coal-miner attempting to save enough coal, which of course is his product, to keep him for life. If wealth could not be saved, or only with great difficulty, future needs could not be provided for, or capital accumulated to raise productivity. Using money as a medium of exchange means that______.