correlation function as a function of separation between grid cells. A non-zero signal indicates the presence of a position-dependent c with power at that scale. The left-hand, middle and right-hand panels show the signal for the G1, G2 and G3 grids, respectively. The x-axis range corresponds to the size of the image in all three panels. The errors indicate the scatter between bootstrap realisations. The middle row shows the weighted mean of and its 68% confidence intervals, determined using all radial bins up to the one of interest. The bottom row shows the p-values of the null hypothesis, with the solid black (red-dashed) line for ().