Measured image position for a full rotation of the instrument at a zenith distance of 60°  taking as a reference (0, 0) the position measured at zenith. X and Y scales are in pixels. Pixel scale is  ~0.15′′/pix for UVB and VIS, and  ~0.2′′/pix for the NIR arm. The dotted circle shows limits set by our flexure specifications:  ± 1 pixel from zenith position. In panels a) and b), corresponding to the UVB and the VIS arm, the curve shows the global motion of the spectral format obtained by averaging measurements obtained with five bright calibration lines. In panel c) corresponding to the NIR arm, the track followed by many individual calibration lines during the rotation of the instrument is shown.