Free magnetic energy – relative helicity diagram of solar quiet regions. Red/blue corresponds to negative/positive total magnetic helicity budgets, while asterisks denote regions centered within heliolatitudes of ±30° and diamonds denote regions centered on higher latitudes. The dashed line denotes the least-squares best fit of Eq. (3). Yellow asterisks show for comparison the free energy – relative helicity diagram of ARs derived by Tziotziou et al. (2012), while the dotted line shows the respective least-squares best fit.