I would suggest subscribing to navlist at fer3.com, and reading through the many old threads there about this subject to get a general idea. In my experience the good and the bad sextants are all mixed on the auction sites. You can always post a picture there before you buy...
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.
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... .