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On Thu, 8 Nov 2007, [iso-8859-1] Wolfgang K�berer wrote:

> Even in the Plath patent description of 1921 the
> vernier is described as being more accurate,
> it says that the micrometer has
> been added to be able to get a quick
> reading when no high accuracy is
> required.

And perhaps Plath was right. I suppose that vernier IS
more accurate, and has fewer week points (backlash,
sea salt ang bugs coming between the teeth and the screw).
It seems that conservative seamen opposed this innovation
(reading the minutes on a drum) and I remember reading
an argument
of some author who tried to convince them that micrometer
is better by the following argument:
reading of micrometer is so much faster that you can
take 3-4 sights with a micrometer in the time required
for one sight with vernier.
By averaging 3-4 sights intstead of one, you achieve
better precision.
Unfortunately, I don't remember where I read this.

Alex.

P.S. I had a vernier C. Plath, and my experience
confirms that reading a 10" vernier scale is a real
pain, especially in poor light, and it indeed takes 4-5
times longer than reading a micrometer drum.

But the main disadvantage of the two old (XIX cent) sextants
I tried was the very poor quality of their telescopes,
incomparable with the modern inverting scopes.
In addition to this, my XIX century C. Plath had a very
non-rigid frame, so after some trial shots, I sold it.

A


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