Galaxy power spectrum measurements and uncertainties obtained from the Flagship I comoving snapshots. Top: measurements of the Model 1 HOD samples. The colour gradient identifies the different redshifts of the samples, as shown in the legend. Dashed horizontal lines correspond to the amplitude of the Poisson shot-noise term P^sn – obtained as the inverse of the number density specified in the last column of Table 2 – for the different redshifts. Centre: same but for the Model 3 HOD samples. Bottom: error-to-measurement ratios, assuming a Gaussian covariance matrix as in Eq. (3). The coloured solid lines are obtained using the Poisson noise-subtracted power spectra, while the dashed black line highlights the linear relationship from Eq. (3), i.e. 2/N_k. Grey bands mark the 1%, 0.5%, and 0.1% limit.