People, don't you read the forum?
Check this out:
http://www.subsim.com/radioroom/showthread.php?t=113775
I was flabergasted when I read that and was wondering why this guy didn't get any responses. Maybe "Sextant Mod, Real Navigation" would have been a better title for his thread. I was about to post a few things but didn't have the time, and neither do I now.
He also posted in the SHIII mod forum about the same mod and some discussion got going. Might want to check this out, too.