Here is the other technique as described by others, however it's not the image with all the steps shown in colors. Can't find that one atm.
With the following technique the writer actually brings you 9km (or whatever unit it is) infront of the target when you are on his track. Since he makes a 9km(nm) circle as targetspeed but sets it up in front of you, instead of the center ON your sub. The center on your sub would make it a pure intercept. But it's allways good to be there early.
http://www.subsim.com/radioroom/showthread.php?t=118988