I've done a bunch of practicing with it, plus the fast-90 method (and I'm trying to get a feel for the vector analysis method, which feels like something the crew of an S-boat would have had to resort to), and I can see you're right now. The damn thing is just inaccurate. If I work up close, it's good enough for a 1500 yard run, which is pretty much how I used to play with auto-targeting.
Wish me luck! Starting a new career with manual targeting, again in the Skipjack