Re: Sight Reduction via Daily Pages in NA v.NA ConciseSight Reduction Tables
From: Hewitt Schlereth
Date: 2011 Jan 9, 10:56 -0400

Alan -

I'm curious about what you have been doing so far to determine the
accuracy of your sights?


On 1/9/11, Gary LaPook <> wrote:
> Here is my evaluation of several methods of sight reduction.
> I learned celestial from Mixter, fourth edition, and this book included
> a complete reprint of H.O. 211 so this is the first sight reduction
> method that I learned. I soon bought a set of H.O. 214 and never looked
> back, H.O. 211 is my least favorite method of sight reduction. Of the
> _tabular_ methods I much prefer Dreisonstok at this point. (But I am
> real partial to my Bygrave slide rule.) When my eyes were younger I
> preferred the Weems Line Of Position Book but I have greater difficulty
> now using the Rust diagram. Apparently others complained about this
> because Weems includes a mathematical solution for azimuth in addition
> to the Rust diagram in the 1944 edition of his book. He made some other
> changes at the same time. He changed the arrangement of
>  table A so now
> each page is entered by latitude not by LHA which adds convenience for
> working a number of sights from the same assumed latitude similar to the
> convenience of H.O. 249, H.O. 218  and of H.O. 214 compared to the
> _inconvenience_ of H.O. 229 (I still don't know why they changed the
> arrangement and ruined a good thing!) He also changed the size of the
> book from a handy 10 by 6 inches to a much larger 14 by 8 1/2 inches,
> not so handy but it does make the printing larger.
> So comparing the various standard methods of paper based sight reduction
> the Haversine- Cosine method takes the most work. The Sine -cosine
> method is a little bit less work but there is the problem with logs of
> negative values of cosine for LHA. Although this method can work with
> some cases, since it cannot be used in all cases it just makes a
> navigator's life more difficult to learn both of these methods. (It is
> probably the best method to use with a calculator, however.)
> I am attaching a list of keystrokes to use in solving this
>  with a calculator. (Note, this corrects a typo in my original
> posting of the keystrokes so the previous version should not
> be used.)
> All the short tabular methods are more convenient than the previous
> two.Of the short methods H.O. 211 takes the most work (although it does
> allow working from the D.R. but this normally doesn't make any
> difference in practical navigation) followed by H.O 208 and the shortest
> solution is the Weems Line Of Position Book.
> The inspection tables, H.O 214, H.O. 218, and H.O. 249 have the same
> arrangement of tables and are equally convenient. H.O. 249 volume 1 is
> especially good when working a round of star sights as you don't need to
> compute individual LHAs so for this use it is better than the other
> tables. H.O 214 includes the necessary factors to allow working from a
> D.R. but you can also calculate these factors for H.O. 218 and H.O 249
> if you need to do this, such as for practice sights from a known
> location. These tables are only
>  slightly faster than the Weems book. All
> the inspection tables take up more space on the shelf than the short tables.
> H.O 229 is not as convenient as the other inspection tables and requires
> more interpolations. However these  tables might provide slightly
> greater accuracy for high altitude sights but this probably makes no
> difference for practical
>  navigation.
> ----------------------------------
> These are links to examples of sight reduction using different methods
> using data provided by Chichester all from the archives for December 2008.
> gl
> --- On Sat, 1/8/11, Alan <> wrote:
> From: Alan <>
> Subject: [NavList] Sight Reduction via Daily Pages in NA v.NA Concise Sight
> Reduction Tables
> To:
> Date: Saturday, January 8, 2011, 9:11 PM
> Given that my efforts at Celestial Navigation are limited to, and unlikely
> to progress beyond standing on the beach, when I can get there, shooting
> whatever happens to be in view, day time and or evenings, it doesn't make a
> whole lot of difference, however I learned to do sight reduction using the
> NA Daily Pages and the Law of Cosines, which strike me as a simple to use,
> direct, straight forward approach to sight reduction.Lately, I have begun to
> delve into use of the NA Concise Tables, a Power Squadron Nav course I'm
> taking requires reduction of sextant sights by both  methods. I understand
> that the Concise Tables Method are supposedly simpler, easier to use.Perhaps
> they are, doing the Law of Cosines absent a calculator, using  log tables
> would be tedious as hell, however as to the Concise Tables being
> "simpler/easier to use", I beg to differ, for it seems that the Concise
> Tables involve endless messing about with and or the massaging of numbers,
> which
>  one doesn't have to do using the Law of Cosines. Of course, I might be
> missing a salient point perhaps more than one here, for instance what
> happens if one's calculator craps out. Of course, with the Concise Tables,
> one would be out of luck if they lost their NA over the side. Seriously
> though, is there something basic or obvious here that escapes me?In
> appreciation of any input or clarification
> offered.Alan----------------------------------------------------------------
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