I stand corrected;
what I should have said is that it is the angle formed by the line drawn from your location to the target's true course. I am sorry for the mis-information.
The problem with measuring the AOB (in real life) is ships zigzag, so what you estimate by periscope as the AOB is constantly changing. Once you know the target's true course, you can then use the AOB, figure out the speed (relative to the true course) and range (relative to the true course); and then you can guess where the ship will be so you can plan your attack. As in all things, including sex, closer is better.
We need practice missions with a merchant ship and a convoy zigzagging at moderate speeds and warships zigzagging at high speeds.
The reason the fast cruiser "Indianapolis" was sunk was it had burned most of its fuel racing the A-Bombs to Tinian and as a result didn't have enough left to get to the Philippines (where it was ordered by MacArthur) unless it cruised without zigzagging.