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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Bubble sextant index error
From: Michael Dorl
Date: 2005 Dec 10, 13:06 -0600
From: Michael Dorl
Date: 2005 Dec 10, 13:06 -0600
So, how do I determine the index error of my bubble sextant without a water horizon? Maybe stand half way between my house and my neighbors house (200 meters between them) and establish a mark on each house at the same level per the bubble. Any departure from horizontal in the bubble will be the same for both sights. Then walk over to my house, place the sextant at the height of the mark and measure the elevation of the other mark. One minute at 200 meters equals 1 * 2 * PI * 200 /(360 * 60) = 0.06 meters = 2 inches; don't think I'll be able to make that kind of distinction. The parallax introduced by the displacement of the prism and the direct view is of that order. Doubt if I can do much better than 3 or 4 minutes.