NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David McN
Date: 2022 May 30, 01:05 -0700
I bought a copy of John Letcher's excellent book 'Self contained celestial nav with HO 208'. He says a primary motivation for him in writing it was to put back into print the 208 tables. He was an enthusiastic supporter of those tables. The tables are elegant to use for typical sight reduction. However, a weakness emerges owing to the excellent extended topics that John includes in his book. He doesn't stop at deriving position lines but goes on to show a number of other practical uses of cel nav: sextant checking by star distances, star ID, finding time from both lunar distances and lunar LOPs, great circle work and so on.
In supporting the 208 tables, he was a little dismissive of haversine based tables that would avoid the need for an assumed position. The 208 tables are certainly quicker to use, but then I found myself spending quite a bit of time over the necessary adjustments to the AP. John uses plotting adjustments for these. So while I was initially quicker with 208, I ended up less accurate and quite a bit slower than the cosine formula by haversine on his more advanced practical topics.
He wrote the book in the 1970s and calculators were recent additions to the tool kit. His conclusion was just use a calculator and DR position. I think for my back up set of tables, Nories haversines still have much to offer. But John certainly opened my eyes to a range of further applications.
