The idea behind it is that you create a list of about 10 - 12 gammas that have about the right spacing for the band you want to search for, and roughly (within 100 keV or so) the right region for the energy of the lowest gamma. You can do this either by using a known band as a template or by running sdgen, a little program to create a .lis file of the standard levit8r/escl8r type. If you do this you can create several files, each with up to 52 lists, each list having a different energy spacing set.
In levit8r, then, you just say "SB a" to test for a band with the spacing of list a, for example. It goes and looks in the cube at all triple coincidences expected from list a, subtracting the calculated background and coincidences from the known scheme, and it tells you what the average remaining counts are, and the standard deviation of the set of remaining counts. From these it works out a rough figure of merit.
You then are given the option of stepping up or down in energy with a loop. That is, the energies in the list can all be incremented by say 2 kev, and the new list tested, incremented again, etc, say 25 times to test the full range of energies for the band. The results are written to the screen, but also saved in the print file, so you can set this up in a command file and leave it running overnight.
Once you have found a candidate band, you can get out of the SB routine and type T a/a to see the sum-of-double-gates spectrum for the new list a (which is modified by the stepping internally to levit8r). You can then fine-tune the gates using the L(ist) command and the cursor on the sum-of gates spectrum.
Clear as mud, huh? I think all this should be clear once you try it. Remember that it won't find SDB's that are in your .gls level scheme, since the calculated coincidences are removed from the net counts. And remember that you can set up gate-list files and command files to leave a search running overnight, for example, to test many possible band spacings. The search results are logged automatically to the levit8r.out file, which you can save and/or print as you exit levit8r.