The part of the spectrum to be under consideration for the procedure is chosen to include all lines to be modeled and is extended on both sides in order to collect sufficient background. The parameter dlam, units Å, gives the range below the lowest and above the highest line. The value of FWHM for each line is limited by the range indicated by dsig (name refers to naming convention prior to version 3.2). The unit system for FWHM can either be Å or km/s depending on the parameter sigunit (0/I). The wavelengths must be in units Å, but the x-axis can be plotted in units keV depending on the parameter ikev (0/I). The four parameters are to be written on the same input line of the parameter file in the order dsig, sigunit, dlam, ikev.