Because an elasticity coefficient is just a number, it is useful to have that coefficient the same for an increase or a decrease in quantity demanded. However, that result might not occur with the example in Figure 3.1 because dividing the absolute change in quantity (ΔQ) by Q1 could result in a quite different number than divid- ing it by Q2. For example, if Q1 = 10 and Q2 = 20, ΔQ = 10. ΔQ/Q1 = 10/10 = 1.0, or a 100 percent increase in quantity.