A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2015 Oct 29, 21:24 -0700
I have a 1937 edition of HO211 and also Agetons 1942 manual in which he adds an additional table. I am attaching an example of that table I and examples from HO208 and Weems Lline of position book. If you compare the tables you will see that Agetons "B" column is the same as the "A" column in both HO208 and in Weems; his "K" is the reciprical of the "b" in HO208 and his "z" is the same as the "z" in HO208.
Ageton HO 211 accuracy 1944 article
From: Paul Hirose
Date: 2015 Oct 29, 13:16 -0700
I have the Ageton sight reduction table in three different books but don't own a bona fide HO 211. Due to recent discussion I thought maybe it's time to buy one. While searching the Web I came across a 1944 article at the ADS site on HO 211 accuracy by Samuel Herrick. He notes Ageton's claim of .5 minute accuracy without interpolation and his caution about hour angles near 90 degrees. So is it safe to infer his accuracy claim is valid whenever the caution is not applicable? No, says Herrick. In fact, the maximum error can reach about 6 minutes without interpolation. A major source of error is the step where you look up function A of side R and take out B of R. (R is the side that is perpendicular to the meridian and common to both triangles.) "The interpolation of B(R) from A(R) will alone reduce the maximum error to about two miles for K = 90°, 0.8 mile for K = 80°, and thus bring the error within practical limits for most navigation problems." "In fine, the maximum error of 30 miles that may be found in the use of Ageton's table without interpolation sets a dangerous trap for the unwary navigator, especially if he be an airman making a sun-line approach at sea. But forewarned, he will find a way to his taste for avoiding it." Samuel Herrick, THE ACCURACY OF AGETON'S METHOD IN CELESTIAL NAVIGATION, Publications of the Astronomical Society of the Pacific, Vol. 56, No. 331, p.149 (August 1944). http://adsabs.harvard.edu/abs/1944PASP...56..149H