The program takes a weighted list (most important targets have highest weight) of target coordinates and inserts them into the design one at a time, where possible, in order of their weight. As more targets are inserted the spectra would overlap. To avoid overlap the position angle of the spectrograph is changed with respect to the target field. A range of position angles (PA) is searched to find the one with maximum total weight with no overlap.
To align the mask to the sky, two setup stars (not necessarily in the field of targets) are used. These stars should be within 10-15 arcminutes of the field center. The program calculates the offset from the easily visible (on the acquisition TV) setup stars to the field center.
The program has a additional feature that will extend each slitlet, where possible, to record extra sky. One pass is made through the target list to design the mask and then another pass is made to extend the slitlets.
Once satisfactory trial solutions have been made, the input files can be E-mailed to email@example.com. He will run the the final solutions and produce the necessary material for fabrication of the masks. The lead time to produce the masks is, at least, three weeks in advance of the run.