NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2010 Feb 17, 12:20 -0800
Brad
You wrote:
"As to the recalled difficulty with different telescopes, I would suggest that this implies a lack of parallelism between the plane of the arc of the instrument and the long axis of the telescope. "
I think I am correct in saying that as the sextant reading approaches zero, so does the error from mis-collimation reduce. At a reading of 10 degrees, for example, Simms gives the error as only about 5 seconds for a tilt of a whole degree (an amount that should be noticeable to most people).
I suggest that those who believe they can correctly estimate their index error to a tenth of a minute on the basis of a single estimate deceive themselves. I would invite them to estimate it thirty times in a row and if they can get the same result within a tenth of a minute each time, I will be among the first to congratulate their instrument.
Kind regards
Bill Morris
Pukenui
New Zealand
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