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

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Re: Sight reduction methods
From: Robert VanderPol II
Date: 2015 Nov 3, 20:23 -0800

Sight reduction methods
From: Dale Bletso
Date: 2015 Nov 3, 12:30 -0800

How many different methods are there for sight reductions.  I have used Law of Cosines, NASR, HO211 (Ageton) and HO229.  I also know of HO249 but have not used it. Just curious.

In addition to various early methods using  Sine&Cosine Tables and Haversine Tables which I have limited knowledge of the following are some of the major manual systems widely used during the 1900’s (at least within certain niches) or that are currently seeing development.  The most commonly used names are underlined:

Bygrave /Air Ministry Laboratories Position Line Slide Rule (1920), Tubular slide rule 3”dia X 9” Long,  Altitude to about 1’ and azimuth to 1o.

Weems Line of Position Book/A short accurate method using Ogura's altitude tables and Rust's modified azimuth diagram (1928)

### H.O.-211/Dead Reckoning Altitude and Azimuth Tables/Ageton (1931) 36 pages, Estimated Position, Tables of Log-secant and Log-cosecant,  Results degrade when intermediate result K is near 90o or 270o. Altitude to 0.5’ and Azimuth to 1o.

H.O.-214 /Tables of Computed Altitude and Azimuth/H.D.#486 (in UK) (1936 -46) 9 volumes, all celestial bodies.  Altitude to 0.1’ and azimuth to 0.1o.  Assumed position.

Brown-Nassau Spherical Computer(1942-5) circular slide rule,12” square X ¼” thick. Assumed position, Altitude to about 5’ and Azimuth to 1o. Solutions worked in about 1 minute of time.

H.O.-229/Sight Reduction Tables for Marine Navigation  (1945ish )Assumed Position, 6 volumes, all celestial bodies, Altitude to 0.2’ and azimuth to 0.1o. (Replaced HO-214 for US Navy use in 1971), double second difference interpolation may be required required for altitudes above 60o .and altitude accuracy can degrade to 0.3’ or so.

H.O.-249/Sight Reduction Tables for Air Navigation/A.P. 3270 in the UK  (1947-53)Assumed position, 2 volumes plus a companion volume of pre-computed stars.  Only works for sun, moon, all planets and stars up to 30o declination.  Altitude to 1.0’ and azimuth to 1.0o.

Doniol/Miniature Navigation Table for Altitude and Azimuth (1955) 2 pages, Altitude to 0.1’ and azimuth to 0.1o

Reed's Nautical Almanac Method

Compact Sight Reduction Tables/Bayless (1980), 9 pages,  Modified HO-211

Sight Reduction Tables for Small Boat Navigation by Hewitt Schlereth (1983), Modified version of HO-229, Assumed Position to nearest even number, bodies to 29o declinations and AP to 59o latitude.

# Davies/Concise Tables for Sight Reduction/Nautical Almanac Office Sight Reduction;  (1984), 32 pages, Assumed Position, all celestial bodies, accuracy degrades when altitude nears 90o.

S-Tables/Pepperday/ Celestial Navigation With the S Table, A Complete Sight Reduction Method for All Bodies in Nine Pages (1992), 9 pages, Modified HO-211

LaPook / Flat Bygrave(2009) Variation of Bygrave, 2 flat sheets,

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