Example of correction for stray radiation for a subregion in the NEP field. Upper panel: dashed curves show spectra taken at different LST (black and gray) with different stray radiation. Each curve is the average of 280 contiguous H i spectra on the T_mb scale; averaging is essential for lowering the noise, to reveal more clearly the effects of stray radiation. Dotted curves: our calculation of the expected stray radiation. Solid curves: spectra corrected for stray radiation, now well aligned. Middle panel: mean difference of the corrected spectra (note that the difference of the uncorrected spectra, or of the stray radiation, would be far offscale). Lower panel: spectra showing the rms of the 280 individual differences before (dashed) and after (solid) the correction for the stray radiation.