The elasticity of supply will generally vary along the curve, even if supply is linear so the slope is constant. This is because the slope measures the absolute increase in quantity for an absolute increase in price, but the elasticity measures the percentage change. This also means that the slope depends on the units of measurement and will change if the units change (e.g., dollars per pound versus dollars per ounce) while the elasticity is a simple number, independent of the units (e.g., 1.2). This is a major advantage of elasticities.