Both precision and accuracy are needed. "Without accuracy, what's the point." The operators manuals for the Davis sextants have instructions for adjusting the mirrors and essentially reducing alignment errors to near zero. With errors removed (implying it is accurate), precision is the question and limitations of the sextant design will determine that attribute. The Davis Mark 3 can be read to 2 minutes of arc which is a built-in precision limit; the Mark 25 can be read to 2/10's (0.2) of a minute of arc (12 seconds of arc if my math is right). I'm aware of one high end sextant that is guaranteed to 9 seconds of arc. If they are adjusted properly to remove alignment errors, they should be accurate too. A lot more money buys you a tad bit more precision.

But what is the requirement for a highly precise sextant when due to motion of the boat (combined with the steadiness and eye of the navigator) the best you can expect is +/- 5 minutes of arc? You can read minutes worth of accuracy to a precision of 12 (or 9) seconds -- so what.

That may be one reason the Davis Mark 3 is actually a pretty good choice. Its price, simplicity and ease of adjustment make it a pretty good fit for a sailboat which is low to the water and constantly moving. OTOH, if you are on a largish vessel where the height of the seas is not as significant, and where pitch and roll are much more reduced, a higher end sextant may be worthwhile. In that case you are probably a salaried navigator who has been working at sea for years and your sextant is one tool in your toolbox.


FWIW, my opinion...