Spatial distribution of the mean number of data points in OTELO pseudo-spectra. The departure from concentric rings around the projected position of the RTF optical centre is an effect of the cross-shaped dithering pattern of individual RTF observations. We note that, for sources located in the vicinity of the CCD gap, the number of data points could be even smaller than the nominal number of slices: only 55 catalogued sources are affected by this contingency.