The core functionality of the original FIVEL program published by DDH was to access the appropriate atomic data, to employ an iterative technique (geometric bisection) to solve for T given N (or vice versa), and to calculate the level populations and line emissivities given T and N ; all for a single ion. We revised the FIVEL subroutines to isolate the data I/O and error handling, so that any number of applications can be layered upon them. The tasks that we built for nebular are summarized in Table 5 . The following subsections summarize the capabilities of these tasks, including illustrative examples. Since this package, like most software, can be expected to evolve, detailed descriptions of the task interfaces and the various task parameters are left to the extensive on-line documentation.