A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2014 Jun 10, 20:38 -0700
This cosine haversine formula was retrieved from my 1977 Bowditch. Mr Doniol is given credit for modifying a previous haversine formula. Formula rules were not given but It looks as if cosine (L-d) is always positive and cosine (L+d) becomes - cosine (180 -(L+d)) when sums are greater than 90°.
Another interesting twist is that accuracy doesn't seem to suffer much when a 10" slide rule is used to perform the one multiplication step This cuts reduction time in half. Trials will be done to verify this.