When TUNE_SKYPOLY>0 it specifies the degree of polynomial to use
when trying to fit to the sky intensity at any single constant-X /
lambda increment. These polynomials are used to predict the
contributory sky intensity in the object pixels.
The default value is TUNE_SKYPOLY=0 to obtain sky averaging
sky model is constant at each order/column).
Set TUNE_SKYPOLY=-1 when there is no sky to be modelled
(i.e., sky model is zero everywhere).
Initial suggested value: 0.
ECHOMOP-Echelle Data Reduction Package
Starlink User Note 152
2003 July 14
Copyright © 2003 Council for the Central Laboratory of the Research Councils