Difference between the helicity variation rate and the boundary helicity flux computed in the practical DeVore gauge. The relative helicity conservation criterion C_r (red line, Eq. (41)) and the magnetic helicity dissipation criterion C_m (blue line, Eq. (42)) are plotted relative to the helicity variation rate (, black dashed line, left panel) and in their own amplitude range (right panel). The inset in the right panel presents the difference between C_r and C_m, i.e., the potential helicity volume variations dH/ dt_p,var.