Personally, I'm better at visualizing or projecting a target path. If you can do that, you can use your scope in SH3 like a whiz-wheel to automatically calculate the AoB for you.
I most frequently develop my firing solutions ahead of time, while enroute to my attack station and many times without any actual visual observations.
I made note of the technique I use in the following patrol report:
10th Patrol of U-53 - Radio Contact Intercept