Sensitivity of Spitzer/IRAC channel 1 data as a function of cumulative area coverage. The coloured lines illustrate 1σ depths measured in empty diameter apertures in each field. The grey solid line is the total area observed to a given depth summed over different surveys. The data points indicate point-source sensitivities at 1σ compiled in Ashby et al. (2018) (we note that some of these data are included in our stacks). The circles and squares represent surveys executed during cryogenic and warm missions, respectively.