# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Sight Reduction via Daily Pages in NA v.NA Concise Sight 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? Hewitt On 1/9/11, Gary LaPookwrote: > 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. > > > > > > > > > > > http://www.fer3.com/arc/m2.aspx?i=106696&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106697&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106700&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106702&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106705&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106707&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106708&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106720&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106721&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106744&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106745&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106747&y=200812 > http://www.fer3.com/arc/m2.aspx?i=106760&y=200812 > > > 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: NavList@fer3.com > 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---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ----------------------------------------------------------------