I am considering buying a sextant but not sure at this stage whether it would be second hand or new. Having looked at a few brochures and on ebay the variation in specification seems bewildering.

Advice on the specification for a new sextant and what to look out for when buying second hand one in terms of condition would be welcome.

John B

John
A few thoughts after dredging up what I thought I’d long forgotten from my time at sea:
A quality sextant should have a certificate with a graph or table of centrering errors against angle. A perfect sextant would have the pivot point of the index arm at the centre of the instrument and when this is not the case, an error usually in seconds is recorded which varies with the position of the index arm. A centering error of 1’ or 60” means you are starting with a 1 mile position error before you start on all the other variables. If you have the calibration certificate that appears genuine then you can atleast allow for the cerntering error in your sight calculations. No certificate, then you have an unknown variable.
Of the other 3 errors, Index error can be measured and allowed for, and perpendicular its and side error can be measured and corrected with the screws on the side of the respective mirrors (plenty of guidance on the procedures on line).
Hope that helps
Regards
Colin