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Peter Fogg wrote:
>>On Behalf Of Lu Abel
>>
>>We're talking about the sextant being a backup navigation instrument,
>>not the primary one, so I must ask why you think a Davis Mk 15 or Mk 25
>>wouldn't be up to the task.
>
>
> Metal is more reliable. Won't warp and is less liable to temperature
> effects. Nothing new or controversial here.

Do you speak from experience or just theory about "plastic?"

My understanding is that Davis's are made out of a form of "engineered"
plastic that is very strong and has virtually no temperature coefficient
of expansion.   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.

Lu Abel

   

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