The 2D product spectrum of nightly acquired telluric standard stars
is analyzed. The PSF of the central positive signal (ignoring both
neigboring negative signals originating from the NIR double subtraction
data reduction method for nodding observation) is fit with a Moffat function for each
wavelength bin. The spectral trace is fit by a quadratic function:
</font><p><font size="2">
trace = ADC_y0 + ADC_y1 * (lam - lamC) + ADC_y2 * (lam - lamC)^2. 
</p>

The mean position of the spectral trace (ADC_y0) and the spectral slope 
(ADC_y1) as a measure of the residual optical distortion  are monitored, ADC_y1 is scored in addition.
ADC_y2 is available in the QC1 DB.