Figure 1. Bland–Altman plot of the differences between bone mineral density measurements at each heel, against their mean. The solid regression line (y=0.015 x -0.015) has no significant slope (95% confidence limits 0.1, -0.07) and is close to the line of zero difference (broken line), indicating that there is no systematic difference between measurements, whatever the bone mineral density (BMD) value. , female; •, male.