Inter-order background subtraction results for GD71. The left panel shows a section of a UVB raw frame (two illuminated echelle orders and the inter-order space between them), with illumination background (including pick-up noise). The central panel shows the same CCD section with applied inter-order background corrections. The corresponding illumination background model is presented in the right panel and its color scaling is illustrated in the bar at the bottom (bar valid only for right panel). The horizontally aligned pick-up noise shows up as a periodically alternating level of reduced and enhanced counts and is accurately fitted by the model. The color scales of all images have been histogram equalized.