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Robert,
In a message of April 6, 13:17:20 EDT
Joel advertized a C. Plath Navistar Classic
on e-bay, as "Their Finest sextant ever".
It has this feature: compensation for the index error.
You can still see the picture by clicking
the link in this cited message.
This is what I was refering to in my message.

On my opinion, this feature is superfluous.
As I understand, C. Plath is famous for the high quality
frame. But I suppose that the frames of this type
of all C. Plath sextants
of the later years were manufactured by the same process.

Alex

On Sun, 14 May 2006, Robert Eno wrote:

>
> Alex,
>
> It is Cassens and Plath that has this feature. To the best of my knowledge,
> C.Plath never had such a feature. As to C.Plath being the best sextant in
> the world, well, it may or may not be true. Having owned both, I'd be hard
> pressed to say that one is better than the other.
>
> cheers
>
> Robert
> ----- Original Message -----
> From: "Alexandre E Eremenko" 
> To: 
> Sent: Sunday, May 14, 2006 3:37 PM
> Subject: Re: sextant calibration
>
>
> >I am of the same opinion (as George and Red)
> > on this C-Plath gimmick: adjusting for the
> > index error. It saves you ONE arithmetic
> > operation in reducing the sight,
> > namely one addition/subtraction (of the Index error).
> >
> > To Joel: is THIS the feature that makes C-Plath
> > Navistar Classic "the best sextant in the world"?
> > :-)
> >
> > Alex.
> >
> > On Sun, 14 May 2006, Red wrote:
> >
> >>
>
> >> George, failing to use a zero-adjustment, after obtaining a sextant that
> >> was
> >> designed and built and sold at extra cost in order to enable you to make
> >> that
> >> adjustment, is certainly possible. You are right. And building one, at
> >> unnecessary expense which places your product at a marketing
> >> disadvantage, does
> >> not mean the user MUST use it. You're right again.
> >>
> >> But failing to use the device, which can and often will eliminate one
> >> potential
> >> source of math error from your reductions, makes absolutely no sense at
> >> all. It
> >> would be what I call "belligerent ignorance", taking pride in NOT
> >> obtaining or
> >> using the information and resources that in this case are literally at
> >> your
> >> fingertips.
> >>
> >> While you've got a sextant in your hands for the first time, and
> >> presumably you
> >> are taking the time to check it for errors and adjust them out, you would
> >> have
> >> to be a particularly stubborn old coot to refuse to use one of the
> >> simplest and
> >> most obvious tools on it to remove one step from all subsequent
> >> observations.
> >>
> >> I expect those people wouldn't bother using a sextant at all, when they
> >> can
> >> simply look at their own feet and announce just as confidently "I am
> >> HERE!"
> >>
> >> ----- Original Message -----
> >> From: "George Huxtable" 
> >> To: 
> >> Sent: Sunday, May 14, 2006 1:34 PM
> >> Subject: Re: sextant calibration
> >>
> >>
> >> > Red appeared to argue with my earlier statement-
> >> >
> >> > | "But one adjustment that does NOT  EVER
> >> > | need to be made is the zeroing of index error, whatever it may be."
> >> >
> >> > in writing
> >> >
> >> > | The Plath companies apparently disagree with you, George. Their
> >> > sextants are
> >> > | built with an extra wheel and scale to allow the user to zero out
> >> > the index
> >> > | error. Would I do this every time? No, certainly not. But it is
> >> > something that a
> >> > | user certainly would do the first time they got the sextant, and
> >> > were trying to
> >> > | set up a baseline of adjustments on it, including the mirror
> >> > positions.
> >> > |
> >> > | More like, to quote Gilbert & Sullivan's Mikado, "Never? Well,
> >> > hardly ever!" 
> >> >
> >> > What I said was that the index error adjustment, to bring it to zero,
> >> > does not ever need to be made, and that's a correct statement. The
> >> > fact that Plath have arranged things so that if you want to adjust it,
> >> > it's easy to do so, does not invalidate what I said. That's not the
> >> > only instrument for which such provision has been made. I remember
> >> > seeing an ebony octant, from the early 1800s, provided with a
> >> > lever-on-lever mechanism for fine-tweaking the angle of the horizon
> >> > mirror, for just that purpose. It provided just the right sensitivity
> >> > of adjustment, and stayed nicely put when you let it be.
> >> >
> >> > But just because you CAN make such an adjustment doesn't mean you NEED
> >> > TO. When Red says it's something "a user would certainly do the first
> >> > time", I wonder where he gets that certainty from.
> >> >
> >> > George.
> >> >
> >> > contact George Huxtable at george@huxtable.u-net.com
> >> > or at +44 1865 820222 (from UK, 01865 820222)
> >> > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
> >> >
> >>
>

   

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