Residual plots illustrating the sensitivity of the TT spectra to foreground modelling. The blue points in the upper panels show the CamSpec half-mission cross-spectra after subtraction of the best-fit ΛCDM spectrum fit to TT+lowE. The residuals in the upper panel should be accurately described by the foreground model. Major foreground components are shown by the solid lines, colour coded as follows: total foreground spectrum (red); Poisson point sources (orange); clustered CIB (blue); thermal SZ (green); and Galactic dust (purple). Minor foreground components are shown by the dotted lines, colour coded as follows: kinetic SZ (green); and tSZ×CIB cross-correlation (purple). The red points in the upper panel panels show the 545 GHz-cleaned spectra (minus best-fit CMB, as subtracted from the uncleaned spectra) that are fit to a power-law residual foreground model, as discussed in the text. Lower panels: spectra after subtraction of the best-fit foreground models. The χ² values of the residuals of the blue points, and the number of band powers, are listed in the lower panels.