Residuals, , between cross-spectra estimated with the baseline mask and those computed with the more conservative masks featuring Galactic latitude cuts |b|< 30° (blue curve) and |b|< 40° (magenta). Residuals on the y-axis are in units of the Gaussian random errors, whose 1σ level is plotted for reference as a horizontal dashed line. The top and bottom panels show the results for the NVSS and TGSS cases.