# NavList:

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

**Re: HO 211 with Sadler method**

**From:**Stan K

**Date:**2016 Jul 27, 01:17 -0400

John,

I was aware of everything in your message (I even put Greg's "method" into a computer program back in October), but maybe I need to state my question another way.

Looking at, say, the 1958 Bowditch, there are dozens of sight reduction methods listed, but I do not know which, if any, corresponds to Greg's "Ageton Classic method". Sure, there are several log-trig types, haversine types, etc., but none seem to correspond to Greg's "Ageton Classic method", even considering forms of the table other than Ageton's, with, perhaps, multipliers other than -100000, adders other than 10, etc. But maybe I'm just missing it. Where is the "method" that simply applies "modified" log-trig values to the classic Law of Cosines formulas to avoid multiplications and divisions? Maybe it just doesn't have a name.

In any case, with a method as simple as applying "modified" log-trigs to the classic Law of Cosines formulas, why did apparently more complex methods even appear, like those that split the navigational triangle into two right triangles? What advantages do those methods have? I always felt that standard or compact Ageton, with all its rules, was quite subject to error, and many dislike the Nautical Almanac Concise method for the same reason. It can't just be table size, because Greg's table, or even the original Ageton table, is pretty small.

Stan

-----Original Message-----

From: John D. Howard <NoReply_Howard@fer3.com>

To: slk1000 <slk1000---.com>

Sent: Tue, Jul 26, 2016 11:55 pm

Subject: [NavList] Re: HO 211 with Sadler method

From: John D. Howard <NoReply_Howard@fer3.com>

To: slk1000 <slk1000---.com>

Sent: Tue, Jul 26, 2016 11:55 pm

Subject: [NavList] Re: HO 211 with Sadler method

Stan,

If I may interject some thoughts about Greg's Agenton-Calssic table. The method did take off - it is the classic law of cosine formula to solve for H ie. Sin H = Sin L Sin D + Cos L Cos D Cos LHA

The Agenton part of the table is that the Log Sin of an angle is multipled by -100,000 ala Agenton. The classic log trig tables added 10 to the log because the log of a number less than one is negative so to prevent navigators from adding a bunch of negative numbers ( and subtracting negative numbers ) they added ten. Greg made a wounderful, easy to use log trig table but no method.

Ageton came up with a different way of computing H by making two right-angle triangles out of the single spherical triangle. His table A and B were the log trig multiplied by -100,000. Easier to use than tables made by adding ten. IMHO

Greg's table is so easy to use because the sin, log sin, log cosine, and cosine is listed in that order. His table can be used for any formula that is solved with sin, cosine, and tan - prime vertical, azimuth, ampltude, etc. Just add A for sine and B for cosine ( A-B for tan)

When the discussion last October was about the Ageton-Classic I kept trying to figure how he was using the Ageton METHOD of two right triangles. Turns out Greg was not.

I have said it befor - I love the new table - I use it ( law of cosine ) as my prefered sight reduction method.

John H.