S/N curves of GD71 in the UVB arm obtained with two different slit widths and two different extraction methods (100 seconds exposure time). The solid black (red) curve shows the S/N of the optimally extracted 1.0″ (0.5″) slit-width data and the corresponding dashed curves show the conventional approach of collapsing the entire slit. We note that the curves have been smoothed so that systematic trends can emerge.