Next message: Frank Reed: "Re: The lost expedition of La Perouse"
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
