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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John D. Howard
Date: 2016 Jul 26, 20:44 -0700
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.
