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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A slope example
From: George Huxtable
Date: 2010 Dec 4, 00:12 -0000
From: George Huxtable
Date: 2010 Dec 4, 00:12 -0000
Peter Fogg would have been better employed in getting his arithmetic right than in demonstrating his command of French. He doesn't provide units for the slope he has calculated of 57, but I will presume that this represents 57 arc-minutes over the 5 minutes of time covered by his plot. Is that correct? However, it's obvious to anyone's eye that the "calculated slope" and the "best fit" lines actually show a rotten fit to the plotted points, with insufficient slope. That appears to be because they have been plotted with a slope of 47 arc-minutes over the 5-minute period, not 57. And it's equally obvious to anyone's eye that the point he has pointed with an arrow as "averaged" cannot possibly be an average value of the 5 plotted points, in altitude and in time. My own averaging of the 5 points given shows a mean time of 16h 30m 11.0 seconds, not very far from his value. But I make the mean altitude to be 69� 12.3', not his value of 69� 02.6'. and if you plot that point correctly, it then sits exactly where you would expect it to, in relation to the original 5 observations. Peter will have to do better if he wishes to persuade us to take his proposed method seriously, as an improvement on averaging. And preferably, next time, in English. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
