The frame to be used for determining the limits of the dekker.
This should be a frame which clearly delineates the inter-order gap
and the full extent of the slit. In general the arc-lamp frame is
used, but a flat-field may also work.
ECHOMOP-Echelle Data Reduction Package
Starlink User Note 152
2003 July 14
Copyright © 2003 Council for the Central Laboratory of the Research Councils