Personally I'd never buy a new one, since a second hand one is just as good (if you have a bit of knowledge and avoid broken ones). A sextant doesn't need calibration beyond what's done at the factory and what you can do yourself. On top of that most have been very lightly used.
If you're interested in the instrument itself (rather than simply how to use it as a tool), 'The Nautical Sextant' by Bill Morris is a superb book: https://www.amazon.com/Nautical-Sextant-W-J-Morris/dp/093983... .
I can recommend American Nautical Services.
That is a typical 'decorative object', not a sextant fit for purpose. They've been flooding auction sites in hundreds of variations, often 'antiqued' and made to look superficially like real 150 year old sextants.
Imagine staring into the sun through that telescope using only that coloured green glass as a filter. Goodbye retina!
There are two courses, actually. The first one focuses on sun sights- I've had that one. The second uses other stars. It's really for marine folks- so it includes a lot of navigation stuff.
It's also sad that we're still using trig tables (that's essentially what the nautical Alamanac is. It also has to be updated every year). I thought the aeronautical paper flight computer was complex ...
Also, I find it hard to believe that a set of 6 books is more disaster proof (and quicker to use) than a hardened calculator for when the shit hits the fan ...
FWIW, here is a nice free resource for printing your own almanac:
For the purpose of astro nav:
NP303 is calculated for an epoch of 5 years (and it's only 3 books). Until its end of life, it has to be "updated" in the sense that corrections need to be applied as they are released.
I don't think the point of the books has ever been disaster proofing. For the most part, books were good enough for the job before computers and still are. They're cheap, come from trusted sources (and it's easy to verify that they're legitimate), and they're easy to correct should they have errata.
Windows PCs and excel spreadsheets are used in navigation all the time. Nobody's forcing navigators to use books. If they do, though, they probably have a good reason for it.
It is a projection and not a list but it’s very handy and helps you identify objects better than a list would.
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