Estimating the noise in a spectrum T using ΔT_pol. Open circles give the standard deviation of ΔT_pol within bins of 2 × 10⁵ data points as a function of T, using spectra from all NEP pointings. This agrees closely with the prediction (dotted line) from Eq. (6) with σ₀ = 0.111 K and T_sys = 20 K. Also shown is the mean of ΔT_pol for each bin.