A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2017 Aug 13, 13:08 -0700
If a lower limb Sun is timed on a Bris sextant image then subtract S.D. and add dip & refraction to the calculated Hc . This gives the Hs calibration. Do not attempt to use a sight reduction table (pub. 229, 249) for this which uses a selected assumed position. Much better to use a navigation computor, usno, or smart phone app with the GPS position as the assumed position.
Give me all your data and I can help generate a calibration diagram for your Bris. Needed: Date, UT time, GPS position, height of eye, Sun limb used ( upper, lower, center ).
Double check the calibration by using a standard sextant to make an observation right after the Bris observation. The Hs readings should be within 3' or 4' difference. Better yet have an assistant with a sextant take a reading on your mark using the Bris.