The physical model is fit to the 9 pinholes arc frame. For each used arc line (there are about 200-400 arc lines times 9 pinholes ) a residual in X (cross dispersed direction) and Y (wavelength direction) can be determined. The median of all residuals in X and in Y are shown. These values express how good the 9 pinhole arc frame is matched by the physical model. (more a quality characteristic of the data reduction). The systematic error in wavelength direction is expressed by the median of all residuals in Y.

Note that offsets of the spectroscopic format between the night time observations and the day time calibrations (< 1 pixel) are compensated by the AFC (attached flexure compensation) frame.