supply of grain in high- and low-yield years, respectively, and S1 shows the average supply. The government buys grain during high-yield years and sells grain during low-yield years. The price is thus stabilized to P3, rather than fluctuating between P1 and P2, as it did before. Side effects The primary action of buffer stocks, creating price stability, is often combined with other mechanisms to meet other goals such as the promotion of domestic industry. That is achieved by setting a minimum price for a certain product above the equilibrium price, the point at which the supply and demand curves cross, which guarantees a minimum price to producers, encouraging them to produce more, thus creating a surplus ready to be used as a buffer stock. The price stability itself may also tempt firms into the market, further boosting supply. The upside is security of supply (such as food security); the downside is huge stockpiles, or in other cases, destruction of commodities. The scheme also makes domestic food more expensive for other countries to purchase and operation of such a scheme can be costly to the operator. Their main advantage, when compared to other forms of government intervention in markets, is that they are a mechanism that achieves its objectives "quickly and directly". History Many agricultural schemes have been implemented over the years, although many have collapsed. Rubber and timber schemes have also been created to guarantee prices for the producers. Ever-normal granaries The "ever-normal granary" form of buffer stock has been instituted in the Middle East since at least Biblical times; reference to such granaries is found in the Old Testament. In Genesis, the Egyptians used an ever-normal granary to stabilize their food market during the seven years of high yields and the subsequent seven years of famine. Building on simpler predecessors and concepts, the first actual ever-normal granary was built in 54 BC. Its name was "Chang-ping can", and its translation provides the English name. It was promoted by Wang Anshi during the Northern Song period and thereafter. Another example of ever-normal granaries is during the Sui dynasty in China (seventh century AD). The system was used in the Han, Jin, Sui and Tang dynasties. When the system collapsed during the An Lushan Rebellion, massive famine and cannibalism broke out. Although not the first to implement this concept, nowhere else in the world was such a system practiced at such