Estimating the noise in the line integral W using ΔW_pol. Open circles give the standard deviation of ΔW_pol within bins of 2400 data points as function of W, using spectra from all NEP pointings as in Fig. 13. This agrees closely with the prediction (dashed line) based on the accumulation of line noise (dotted line) and baseline errors. Note that the baseline error is dominant in measurements of W, even though it is not dominant for measurements of the spectrum T (Fig. 13). Also shown are the data (filled circles) and the prediction (lower dashed line) for the mean ΔW_pol.