It's probably not what you used, and is based on the math behind those advanced mapdrawing tutorials. But it is a no-brainer to get AOB (and from that course) of the target with it. Just slide those wheels. You need patience for it though. The time interval should be
atleast as long as it takes for bearing 2 to move 5 degrees from bearing 1. Longer makes the AOB more accurate.
AOB at bearing 3 is: the AOB in the readout window and add B3-B1 to it.
http://www.subsim.com/radioroom/showthread.php?t=147719