Correlated noise model. In grey are shown the cross-detector TT spectra of the half-ring difference maps. The black line show the same, smoothed by a Δℓ = 200 sliding average, while the blue data points are a Δℓ = 100 binned version of the grey line. Error bars simply reflect the scatter in each bin. The green line is the spline-smoothed version of the data that we use as our correlated noise template.