Re: practicing with sextant on land
Celestaire makes a practice sight for the 3b. I think they're about 50 bucks or so. I got one so I could teach my sig other. It takes a fair bit of practice with them to actually start getting fairly accurate, but like the saying goes: your first 1000 shots will never be as accurate as your second 1000 shots.
The sight has a leveling bubble inside with a coresponding horizontal hairling that acts as your horizon.
One bonus I found after using this practice sight for awhile: I's amazing how steady and accurate your sights are with a scope on after using this practice sight.
I do find that during times of twilight it can be difficult to locate stars of lesser magnitude because of the lack of light that enters into the sight, but overall for the price I think it a worthwhile purchase.
3500 ft is a fair elevation, but remember that all of those atmosphereic corrections within the nautical almanac are average constants anyway.
How do you like the 3b anyway? I think it a fantistic sextant for the price. I've used many different types while in the Canadian Navy, and I think it rivals anything that they've got. How do you think the full two-way mirror compares to the half mirror?