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I'm not so sure that I could have pulled of Chichesters feat in a Moth bi-plane, see:

http://fer3.com/arc/m2.aspx/Precomputing-sextant-observations-sea-LaPook-jan-2014-g26754

http://fer3.com/arc/m2.aspx/Precomputing-sextant-observations-sea-LaPook-jan-2014-g26746

gl
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On Thu, 6/12/14, Francis Upchurch  wrote:

 Subject: [NavList] Re: First sight reduction tables
 To: garylapook@pacbell.net
 Date: Thursday, June 12, 2014, 10:01 PM
 
 Not my specialist
 subject, but I'm interested in why RAF preferred Air
 almanac tables to Bygrave at beginning of the
 war. Chichester, great Bygrave user in 1931, was
 teaching RAF navigators in 1940 only using the new
 "secret" Air Almanac tables. No mention of the
 Bygrave in his little book"The observers book of
 astro-navigation part one". On page 86, suggests they
 were based on 1918 Davis tables from US and later US HO 214.
 apparently Weems acted as a consultant to UK RAF during late
 30's and was very influencial, pro tables. (214). On
 page 100 Chichester also recommends the Haversine method
 over the cosine formula because of LHA >90o is
 negative with cosines but always + with haversines.He says
 neither suitable for air work during flights because likely
 to make mistakes with 5 figure logs etc.(He said similar
 during the1931 Tasman sea flights.Here he used the Bygrave.
 the Air almanac not then available. Would he have used them
 if they were?)Gary LaPook and I  recently
 "re-enacted" (me from the comfort of my arm chair
 though) his famous flight using his original chart and
 our Bygraves. remarkably , we both got perfectly similar
 results to Chichester! Beached this year waiting surgery
 (next week now!) , this was the best fun I've had with
 my Bygrave for years! thanks Gary, who showed me how!) I
 suspect Gary could have done it in an open
 byplane!Having used both the tables and the Bygrave,
 I'm still not sure why the Bygrave was not mass produced
 (but wiith a simple lock to prevent slippage, the only
 fundamental design flaw). The scales could have been mass
 produced easily photographically and the rest is basic
 simple craft skills. Best wishesFrancis
 
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