2.3.2—PES formula

PES = % change in quantity supplied / % change in price. Substitute percentage changes consistently and report the coefficient with its interpretation.

For a finite change use the method specified by the question; the midpoint method can avoid endpoint bias. Keep the sign and units clear, although PES is often positive.

A 12% price increase causing an 18% rise in quantity supplied gives PES = 1.5, an elastic supply response.

Do not use the absolute change in output over the absolute change in price and call it PES; elasticity is a percentage ratio.