NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Michael Bradley
Date: 2023 Apr 4, 00:37 -0700
Hello Art, hello Frank
Re the 5 arcmin or so error found by Frank's analysis: perhaps sextant IE problems.
Clue1 'SNO-T one from a selection of sextants'
Clue 2 ' Fogging ' conditions, i.e. quite cool out there
Years ago I was calibrating cheapo sextants by star to star distances ( never understood why reporting it caused such an uproar on Navlist, another story... ).
During that exercise, for each sextant I tested, I checked the index error between each of a run of star to star sights.
One particular sextant had an IE which moved much further than 5 arcminutes during a run of sights in the dark of the night.
So, Art, it might be that one of the IE critical basic adjustments on your SNO-T moved in the relative cold of the night.
Something needs tightening up. Perhaps a mirror retention spring.
It's worth checking the IE on your collection of sextants by repeated 'star on itself' method in the 'cool of the night'.
Perhaps.
Michael Bradley
