Assessing the efficiency of Mexican hats to compute the power spectrum of a field with arbitrary masks by computing the power spectra of 1000 realisations of a random field with known power spectrum in various ring regions. Left panel: regions of interest overplotted on a single realisation of the known random field with the A2319 exposure map. Right panel: recovered power spectra in the various regions of interest for 1000 realisations of the known random field, and comparison with the input power spectrum