Even if they're zigzagging 30 degrees either side of the base course it's pretty difficult to get closer than "20 to 40 degrees port" from 10000 yards. Coming along without zigzagging can you really tell the difference between AOB port 5 and AOB port 10? Even at close range you can tell if it's not zero when you can see part of one side or the other and not just bow on, but anything more accurate than "less than 30" or "more than 30" or "about 60" would take psychic powers. You can get a GENERAL course from AOB and tweak it later by making a second mark and drawing a line through it, but when it comes to shooting at close range you simply don't have time to do anything other than preset the AOB to 70 or 80 and leave it alone.
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