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After you complete the 1D wavelength fit, the code projects this onto a 2D wavelength map, using information about the curvature of the slit image in detector coordinates. As a check, the code plots up an image of the slit illustrating slitillustrating the quality of the slit curvature fit:
The fit is shown as black lines tracing the profile of each arc line used in the solution. If these do not trace the curves properly there is a problem. In this event you should try another arc exposure, and if this doesn't work, contact the instrument team for help.
You are now finished with the arc solution. A file named Arcs/ArcImg****.fits.gz is generated in the reductions directory. This contains the 2D wavelength map, along with additional extensions encoding information about the fits to wavelength and spatial curvature. Time to move on to object finding.