Comparison of flux at the base and the flux at the apex for the six-sided flux tubes. This plot demonstrates that flux is well conserved for most of the "tubes" and therefore the approximation we make for their cross-sectional shape holds for most of them. For further analysis, we discard those tubes for which the fluxes differ by more than 50 G pixel ² (414 flux tubes out of a total of 9050, or about 5%). The 414 discarded points are plotted in gray and the remaining points are plotted in black.