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Re: Freiberger sextant
From: James N Wilson
Date: 2012 Aug 13, 14:49 -0700
From: James N Wilson
Date: 2012 Aug 13, 14:49 -0700
Ridge:
I agree wholeheartedly. You've stated the case very clearly. I would bet
that if you applied your test with a sextant with a vernier, you would get the
same results!
I'll repeat myself, noting that with the vernier you have the opportunity
to read from its wrong end, introducing an eleven minute error. A big price to
pay for an almost nonexistent increase in accuracy.
Maybe I should clarify. Without a vernier, there is only a single index
mark, impossible to mistake, where with a vernier the user has two
choices. One is more obvious, but I wouldn't take note of this if it hadn't
happened. Once is too often. Verniers are worse than nothing.
Jim Wilson
On Mon, 13 Aug 2012 17:08:07 -0400 Ridge White <whiteinstruments@gmail.com>
writes:
Hi Jeremy,You mentioned wishing your Freiberger could be read to .1', a tenth of a minute.In our many years of selling and servicing sextants of many types, we are often asked about the desirability of a vernier scale - instead of just an index mark - opposite the micrometer. A number of times I have pulled from our display a sextant without a vernier scale and have arbitrarily turned the micrometer drum to some position, at which time I ask the customer to read the micrometer drum against the index mark. Three times out of four the customer and I agree. When we don't, we differ by one tenth of a minute. Interpolating is something we do all the time.Given the likelihood that no sextant can repeat a reading down to one tenth of a minute because of tiny amounts of "slop" between the tangent screw and the limb, vernier scales strike us as maybe desirable - but by no means necessary - for accuracy.Just one man's opinion. Anyone else have thoughts on this?Ridge White
Robert E. White Instruments
PO Box 775
Medfield, MA 02052
Tel: 617-482-8460
Fax: 617-482-8304
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