A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2020 May 23, 04:17 -0700
For decades, if not centuries, sextant Manufacturers have been publishing Eccentricity "Calibration" corrections in arc seconds while most generally the verniers show [sub-]arcminutes.
Why so ? Big mystery to me .
I suggest that you start sitting down and first make your own curve applicable to your own sextant in tenths of arc minute as a function of Instrument angle. Or better, write down the "border" values inside which the eccentricity remains constant (exactly like the NAL Altitude Corrections).
I do not know what Bill Morris from New Zealand - our Sextant Expert - would think of such Eccentricity calibration certificate. It seems to go a bit high on one end : nonetheless as long as it stays inferior or equal to 0.1' below 90°, I would not worry too much as I think that this sextant should be ok.
Your advice here, Bill ?
The greatest unknown like for any sextant .. has it been dropped onto the ground, or has it been hit by something hard ?
Shocks can remain totally invisible to the naked eye, and nonetheless they can totally ruin a sextant. In doubt, get it calibrated again.
Only practice from known places first will show you its real value. After 100 shots, you can start being comfortable with a sextant, or start having firm ground to be cautious ...
Good luck !
⚓ Kermit - antoine.m.couette[at]club-internet.fr ✈