Specifies the degree of polynomial to use when trying to fit to the sky intensity over the whole order at a spatial increment.
This facility will be most useful when the sky is very uniform, or possibly when trying to model the scattered light in the inter-order region. The intensities predicted by the wavelength-dependent model are used as input to the spatial model only when they fall within a user-defined distance from the observed value, and when they are not possible sky-line features.
(See also TUNE_SKYLINW and TUNE_SKYLTHR).
The default value is 0.
Martin Clayton