I tried loading this mod, and it appears to be pretty generic, mostly what box you're in, maybe giving you a head's up on which part of the box you're in if you're very careful in your measurement... real life sextants can give you "almost GPS accuracy" according to some studying I did.
though it does require a very good, calibrated sextant, a watch set to GMT to the second, and some very careful usage practices... none of which you can get in the game....
