It's a good question.
Elasticity is the measure of how responsive something is to influence in a market.
Price elasticity, for example, is computed as a ratio of the change in quantity supplied to the change in price. A good is very elastic if suppliers rush to supply more of it in response to increased demand. A good is very inelastic if the supply tends not to respond to a price increase. The ultimate degree of inelasticity, of course, is the case of land. Is it true that for the co-efficeient of elasticity to be useful to decision making, the point elasticity must equate the Arc elasticity.