Elasticity measures how responsive buyers and sellers are to changes in market conditions like price and income. Price elasticity of demand is calculated as the percentage change in quantity demanded over the percentage change in price. Demand is more elastic if there are substitutes, if the good is a luxury, or over a longer time period. Supply is also elastic over the long run as producers can adjust production. The discovery of a more productive wheat variety would shift the supply curve right, lowering the price and total farmer revenue if demand is inelastic.