Elasticity

Consider quantity demanded of a particular good, say, xylophones.  Let’s label the demand for that good x.  Demand for xylophones – x – is likely to be affected by (in other words, a function of) the price of xylophones.  Let’s call the price z.  Calculating the elasticity will tell you how much demand for xylophones changes when the price for xylophones changes, assuming everything else stays the same.  The elasticity of demand (in this case) is the percentage change in x in response to a given percentage change in z.  Elasticity is a number – it has no value.