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I just re-read my message and found an error:
of course 0.2=12", not 6" as I wrote several times.
Below is corrected message:

On Mar 11, 12:16 am, "alex"  wrote:
> > I like seeing the raw numbers!
> > Fred
>
> Here are some preliminary tests of the old vernier
> C. Plath. After collimation adjustment.
> March 10. IC from Sun, average of 3:
> IC=-50", 4SD=64'42" True value 64'.4=64'24"
> March 11, IC from star (Rigel) -1'10".
> GMT 2 a.m. Star distances (corrected for IC=-1'10")
> Betelgeuse-Rigel: 18d35'50", error 14"
> Betelgeuse-Sirius:27d05'30", error -6"
> Betelgeuse-Sirius:27d05'30", error -6"
> Betelgeuse-Sirius:27d05'40", error +4"
> Aldebaran-Sirius: 46d01'50", error -2"
> Aldebaran-Sirius: 46d01'55", error +3"
> Aldebaran-Sirius: 46d01'50", error -2"
> The scope used was 12x, inverting.
>
> Here are the results with SNO-T, 6x inverting scope:
> March 11, IC from star (Rigel) -0.5
> GMT 3 a.m. Star distances corrected for IC=-0.5'
> Betelgeuse-Rigel: 18d35'.5, error +0.2=12"
> Betelgeuse-Rigel: 18d34'.8, error -0.5=-30"
> Betelgeuse-Rigel: 18d35'.4, error +0.1=6"
> Betelgeuse-Sirius:27d05'.6, error -0.1=-6"
> Betelgeuse-Sirius:27d05'.8, error  0.2=12"
> Betelgeuse-Sirius:27d05'.6, error -0.2=-12"
> Aldebaran-Sirius: 46d01'.2, error +0.5=30"
> Aldebaran-Sirius: 46d01'.6, error +0.4=24"
> Aldebaran-Sirius: 46d01'.6, error +0.4=24"
>
> So, as I expected, a vernier sextant seems more
> accurate, but of course it is MUCH harder to use.
> The mirrors (and filters!) are very small. It is hard to catch
> the star, unless you preset the distance. The telescopes
> have very tiny field of view, it is hard to keep the two
> stars in the field. The picture is good only at the center
> of the field, and only if your eye is at the center of the eyepiece.
> I suppose that on a small boat I could use no telescopes, only the
> zero-tube. Only the 12x inverting scope can be used for IC with
> Sun. For all other scopes the shades are too small and let the
> Sun shine straight to your eye.
> In SNO inverting scope you see the sky like in a wide screen cinema:-)
> No need to preset the distance, you can just scan the sky.
> The scale of the C. Plath is very hard to read, especially at night.
> With SNO, reading a scale to 0.1' takes few seconds,
> even without light, while on the
> vernier sextant, more than a minute. You have to look VERY carefully
> to read the scale to 10" (approx 0.2'). And it takes time.
> Roughly speaking, a series of 5 observations of the same distance
> takes 3 minutes with SNO and 10-15 minutes with the vernier C. Plath,
> mainly because of the slow reading of the vernier scale.
> Finally SNO is light, while the old sextant is heavy, and my hand
> shakes,
> especially with a 12 x scope.
>
> Shortly speaking, it is a very different experience with these two
> different types of sextant.
>
> Alex.


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