The document discusses methods for calculating price elasticity of demand. It describes the total outlay method developed by Alfred Marshall, which calculates price elasticity by comparing total expenditure on a commodity before and after a price change. It also outlines three possible results from this comparison: elasticity greater than 1 if expenditure moves in the opposite direction of price, elasticity equal to 1 if expenditure remains unchanged, and elasticity less than 1 if expenditure moves in the same direction as price. Additionally, it mentions the percentage method, which calculates elasticity as the percentage change in quantity demanded over the percentage change in price.