Evolution of the mass-to-flux ratio as a function of time in a slice perpendicular to the z axis, centered on the location of the maximum density at a time of 1.44 t_ff. The mass-to-flux ratio was computed for all cells within a 0.2×0.2 pc² area. With the black points we show the 50th percentile from all pixels in the region and the error bars represent the 16th and 84th percentiles, respectively. With the red points we have zoomed further in to the location where the density eventually increases. The area of this region is 0.01 pc². The dashed red line marks the initial value of the mass-to-flux ratio in the simulation.