Demonstration of probabilistic limiting magnitude measurement. The upper panel shows the distribution of summed counts for a random set of pixels close to the expected source location. Bottom left panel shows a cutout of the transient location; pixels marked in red are excluded when creating the distribution; note the source off-centre is masked. Bottom right panel is the same image with injected PSF sources (marked with red circles) with magnitude equal to the F_ul,β=0.75 limiting magnitude (see Appendix D).