... Up: Data Processing Systems . ... At this point it is indispensable to be able to obtain the measurements of reference features in experimental data such as the wavelength calibration lines with a comparable intrinsic accuracy and repeatability. ... An example of such data is shown in Figure 1, a 70 by 50 pixel window around two ``bright'' calibration lines (slit images) with a maximum photon count of 40 in the brightest pixel. ... Figure 1: Typical photon count distribution for two calibration...