NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: GPS shortcomings.
From: Frank Reed CT
Date: 2005 Jun 11, 03:08 EDT
From: Frank Reed CT
Date: 2005 Jun 11, 03:08 EDT
Lu Abel, you wrote: " I'll agree "metal is more reliable," but by how much? I have co-taught USPS's celestial courses for many years and about 90% of our students have used Davis sextants. In years of checking sights I've never run across one that was off because the sextant was off -- any errors have always been traced to student error. My own Davis Mark 15 is almost two decades old and has never given me a problem." So how do they compare? Can you do some tests? Try this: get out your Davis plastic sextant and any decent metal sextant. Take a couple of dozen sun sights alternating between the two instruments and compare the results. When I have done this, I generally find a scatter of about two to three minutes of arc around correct, calculated values with a Davis Mark 15 plastic sextant and about 0.5 minutes of arc with a metal sextant. If few minutes of arc error doesn't bother you, then a plastic sextant is just fine. I own one plastic sextant and three metal sextants (though two of these are temporary investments). -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
