Average relative error (black crosses) between the [C_II] APS measured in the 54 Uchuu sub-fields masked with r_σ = 3 as a function of spatial frequency, k, at z = 5.2 (top), z = 6.5 (middle), and z = 7 (bottom). The mean errors over the k modes are < 1%, 7%, and 8% for each redshift, respectively. The dispersion (red error bars) normalized by the square root of the number of realizations is also represented. The mean sizes of these normalized error bars over the k modes are 3%, 4%, and 5% for each redshift, respectively. For reference, the equivalent normalized error bars for a perfect Gaussian diffuse signal from the same number of Monte Carlo realizations are over-plotted in blue.