Elasticity of supply must be carefully distringuished from the slope of the supply curve. Supply curves of simple forms have elasticities varying greatly from point to point, whereas curves with simple elasticity functions (constant, linear) do not seem to satisfy the conditions usually postlated fot the supplies of commodities or the factors of production. Elsticity of supply does not indicate relative changes in receipts of costs. For theorical problems, the slope of the supply curve is more useful as an anlytic tool than elasticiy of supply