Left panel: comparison of the evolution of magnetic energy (, black line) in the volume with the time integration of the Poynting flux through the whole surface of the domain (, red line). Right panel: comparison of the evolution of helicity obtained by volume integration (, black dashed line) with the time integration of the helicity flux through the whole surface of the domain (, red line), computed with the practical DeVore gauge. Their difference is plotted in orange on a different range of amplitude (cf. right axis).