Specifies the reject-threshold for sky pixels.
Sky pixels which deviate by more than TUNE_SKYRTHR sigma from the fitted polynomial model, will be clipped, and the model re-fitted.
The polynomial model of the sky background is made by fitting a polynomial at each X-increment. These polynomials are then used to estimate the sky signal level at each spatial sample.
INITIAL SUGGESTED VALUE: 5.0.
Martin Clayton