A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2020 Apr 13, 14:58 -0700
The lockdown is giving me time to study various tables in detail. For example, I have learned that Aquino (HO 200) allows use of the DR position rather than requiring an asumed position. The same applies to Ageton (HO 211).
I took several sun sights and decided to reduce them using Hughes' tables. The first step was to learn Hughes' method. After I had successfully worked one sight I performed sanity checks with AP3270 (HO249), HD486 (HO214), NP401 (HO229) and the cos formula. Then I decided to try HO 208 Dreisonstok. I found that these tables are similar to Hughes' but with one big difference - the meaning of dec ~ lat.
Back on 21st June 2016 Franks wrote (dec ~ lat) = abs(dec - lat).
The worked examples given in the tables show that
Hughes K~d = abs(K-d)
Dreisonstok d~b = abs(d+b)
I have worked the same sight with both Hughes' and Dreisonstok and can confirm these conventions.
With reference to d~b, page 69 of Dreisonstok states ".......add if the signs are alike, subtract if unlike."