Howdy, Hitman.
I may be behind the "curve" on this, but,
Using your side of the Submarine Attack Course Finder/Is Was (SACF), and in reality it is nothing more than a Circular Sliderule with Sine scale only, it can also be used as an ASPECT RATIO (AR) tool:
As we know, all the AR are based on a 90° AoB.
1) After IDing the target ship and obtaining it's AR, adjust the center wheel of the SACF, placing the 90° mark under the AR of the target.
2) After obtaining new AR thru objective lens of the scope, use the clear cursor, sliding it to the new AR and reading the Aob under it.
Using the "Tool" eliminates any pause-the-game math.
Here's a pic: