EBM makes a valid point, a book on my need to-read list, and something from the "The lips keep moving and the lies pour out" files...
I happened to be checking out the Celestaire website last night and happened to notice they had the Davis Mark 3 sextant on sale.
If you're considering getting into celestial navigation the Davis Mark 3 is just the thing to do it with and you might check out Starpath's GPS Backup Kit as a guide for the other bits you'll need to make it all work.
Listening to Sylvie Simmons
So it goes...