AOB is an easy concept in fact, it just requires a bit of practice...think of it like this:
Look from your bridge, TBT or scope at the enemy vessel. AOB is just how much his bow is deviated (Left or right) from pointing directly at you. If it is pointing directly at you, the AOB is zero, if the ship is completely perpendicular to your line of sight to him, it is at a 90º AOB (Which you will recognize easily because his masts and cranes appear thin, each side hiding the opposite, and you only see the sides of the superstructure and no part of the front/rear of it).
The difficult part in determining intermediate AOBs, which people usually fail to recognize, is that the AOB change is NOT linear with the amount of ship you are seeing. Let me explain that a bit: A ship that extends over, say, 10 marks of your scope at a 90º AOB will not extend 5 marks at an AOB of 45º, but instead some 7 marks. The 5 marks would instead correspond to a 30 AOB instead....
But people usually think when seeing a ship so angled that it apparently is only half visible "Oh, it is half as visible as normally, then it's 90º/2=45º". And that's incorrect! The variation in the aspect of the ship when it is angled will not follow a linear curve but instead a Sine curve
So to determine AOB by simple visual estimation, there is no substitute to practice....though here is a quick hint to help you: When looking at a ship you have IDed with the recognition manual, compare the silhouette of the book (Always a 90º AOB, a you see a perfect shot of the side of the ship) with what you see and think how much it is shorter than when viewed from full broadside. Is it about one half? Very well, that's a 30º AOB. About 3/4? That's about 45-50 AOB. Anything in between one half and the plain bow (zero AOB) you can set 15º, and anything between 3/4 and the full broadside length you can set 70º and you will be OK for a first approach.
