Profit can calculate the velocity shift for a spectrum if told what atomic line to use for v=0. To switch into velocity space, generate a list of potential lines using the Line ID button, and then select a likely line from the Line List Window by clicking on it. At this point, the line should highlight, and the Info button and the Velocity radio buttons will also activate. Clicking on the Velocity button in the second line of the ``Button Bar'' will put the plot into velocity (km/s) coordinates with 0 km/s centered on the selected atomic line.
By default, switching to velocity plotting forces the spectral range to be -3000 to +3000 km/s. However, these values (-3000, +3000) can be changed to the users' specification in the FilePreferences window. In addition, if desired, the ``forcing'' effect itself can be eliminated, and the entire displayed spectrum simply transformed as it is with the energy and wavelength buttons.