The ``Line ID'' button fills the Line List Window with a list (based on the atomic database in use) of the lines or features in the selected range shown in the Main Plot Window. The list includes the line position (either in energy (keV) or wavelength (Å) units, depending upon the current display), the ion emitting the line, the energy levels involved, and an estimate of the line strength relative to the strongest line in the list. Currently, two databases are available, either the ATOMDB (http://asc.harvard.edu/atomdb) collisional plasma database or the XSTAR (http://heasarc.gsfc.nasa.gov/docs/software/xstar/xstar.html) photoionized database. The line emissivities are calculated by considering a range of either temperatures or densities and using the peak intensity. As a result, these intensity estimates can be misleading and should only be used as a rough guide when identifying lines.