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Fred:

> One needs to check IE each time the sextant is used.  But one doesn't
> need to ADJUST IE to zero each time.

I would agree in principle (and the explanations for not doing so certainly
do make sense), but am curious why Davis would say that index error should
be adjusted each time it's used? Maybe what they're actually doing is
encouraging people to wear out the adjustments earlier so they'll sell more
sextants?...  ;-)

BTW, does anyone know what kind of accuracy is possible with the plastic
sextants? Is it possible to get a consistent zero (or very low) intercept to
a known position, or with plastic construction are there just too many
variables involved? I did notice that my index error varied over the weekend
from around +5' to around -4' over just a couple of days.

Temperatures ranged from mid-70s (my backyard) to mid-60s (beach), but I
wouldn't think that would be enough of a gradient to cause that much change
(or maybe that's typical for plastic?). The sextant wasn't dropped or
handled roughly (and was always carried in its foam-surround case), so I
don't think mechanical shock would be the cause.

--
GregR

   

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