You are talking about using the fixed wire method, and the Stoppuhr, right?
It's counter-intuitive, and we've all been there, but really AOB is irrelevent. This is because the ships' length is the same whatever the AOB is, and once the ship has covered it's own length, that's all that matters. So long as you can estimate the ships' length.
This is not the case for very small AOB's however. You must have a clear view of both the stern and bow of the target for this method to work
joe
welcome to SUBSIM btw