Left: a comparison of the difference in brightness between the target star and comparison star and the ratio of the out-of-transit precision measured for 330 light curves observed on 22 separate nights using both the comparison star method (σ_COMP) and the CMI method (σ_CMI). On average, we find the CMI method improves light-curve precision by a factor of ~1.5 for comparison stars within 1 mag of the target star or brighter. We only found the comparison star method to improve the precision on seven out of 330 light curves. Right: the achieved dispersion in the light curve of WASP-33 b observed on 2022 September 8 when using the CMI method (black; σ = 3 × 10⁻⁴) and when using a traditional comparison star method (red; σ = 3 × 10⁻³). We find a factor of 10 improvement in out-of-transit precision quality when using the CMI method for this light curve.