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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Testing pocket sextant
From: Bill B
Date: 2006 Jun 14, 02:03 -0400
From: Bill B
Date: 2006 Jun 14, 02:03 -0400
Alex wrote: > The suggestion that the arc is wrong near zero cannot be excluded, > but then this is my second sextant with the same defect:-) > Am I so unfortunate that all sextants I buy have bad arc near zero? > :-) Not likely ;-) If I recall from your beach shots with the SNO-T last year there was an apparent systemic error. We talked about wave height at Hunter's Pub. Maybe 2-3 feet? You initially claimed that was insignificant. We worked out the dip, and tangent via distance vs. wave height, and it about nulled out your error. My impression at this stage of my development (outside of the problems inherent in observing from a medium-displacement small craft, almanac roundings, and blunders) is that accurate dip (both knowing your exact height vs. the horizon and atmospheric anomalies) is the major stumbling block to 0.2' to 0.4' accuracy. I reference Frank's beach shots of Chicago from an Indiana shore, and our inability to resolve the discrepancies. (Although, in my opinion not fully pursued due to lack of list interest. I am excited about George's latest find.) Bill
