A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2014 Nov 6, 09:08 -0800
"Regarding the semi-diameter question, if I shoot using a natural horizon, then I need to +/- one semi-diameter, 16’. If I’m shooting limb to limb using a tray of oil, do I +/- 16, 32, or 64’?"
After dividing by two then you have Hs. Treat as a standard Hs and apply semi diameter of 16'. Don't forget to correct Hs for refraction also.