Median offset and percentiles of the difference between spectra of the same regions from overlapping pointings. The statistics have been computed from a set of 249 regions covering the full PHANGS-MUSE sample, and the resulting percentile vectors have been filtered to make it legible (keeping the sky line residuals visible). Top panel: percentiles of the distribution of the bias level, normalised by the typical (overlap-region-averaged) noise level. Ninety percent of the spectra have a normalised bias that is typically between 30 and 50% of the noise level, while a small fraction show up at levels of 60−120% of the noise, specifically in the blue or red part of the spectrum. We note that although beyond 7000 Å residuals are heavily contaminated by sky line residuals, the pipeline still constructs a roughly correct noise vector. Bottom panel: percentiles (50, 68.3, 95.5%, and 99.7%) of the distribution of differences normalised by the individual spectra noise level, after subtraction of a wavelength-independent median bias offset (see text). The dashed (respectively, green, yellow, and red) lines show values of 1.12 (12% above 1), 2.24, and 3.36, showing that the noise level is slightly underestimated (by about 12%). A trend is visible towards the redder and bluer end of the wavelength coverage.