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Fred,
But this is exactly what Frank originally proposed:
to put the sextant on a table. (How else can you do this?
If the distance to the screen is 15-25 feet,
changing the sextant position even by few milimeters
will matter.

In my experiment, I use two tables approximately of the same height.
On one I put the laptop, and sextant on the second. Then I finely
adjust the sextant position, with pieces of paper under the legs,
so that the screen is visible inside the rectangle of crossed
wires in my telescope.


Alex.

On Sat, 10 Dec 2005, Fred Hebard wrote:

> One other question I have is, why not lay the sextant on a table or
> counter to point it at the screen?  Then it would be as steady as if
> it were on a tripod.  You would have to move the screen to the right
> height, and you would need vertical lines separated by  some
> horizontal difference, but that's not difficult.
>
> Fred
>
>
> On Dec 10, 2005, at 12:04 PM, Alexandre E Eremenko wrote:
>
> > Dear Frank,
> >
> >> No, I haven't yet.
> >
> > Tell us the results when you do.
> >
> >> I think the method works  despite the parallax issue.
> >> The only assumption is
> >> that the measured angles  should be increasing linearly.
> >
> > It is exactly this assumption I had doubt about.
> >
> >> The fact that the
> >> pattern repeats with a one  degree period over two full
> >> degrees of measurement
> >> gives me some confidence that  this technique
> >> is measuring something involving
> >> micrometer error. What else  could produce such cyclic behavior?
> >
> > That's a strong argument. I will be totally convinced when you measure
> > another sextant which will not show the sinusoid pattern.
> >
> > I made a try yesterday, but instead of the expected sinusoid pattern
> > I obtain something which looks more like "white noise".
> > The interval between the lines was 2.3' and I made one full turn.
> > The distance was approx 16 feet, and the mean quadratic deviation
> > of the measurements was 0.17'. But there was nothing resembling a
> > sinusoid pattern.
> >
> >> Looking at all those lines and their  reflected images through the
> >> sextant
> >> drove me nuts so I switched to the "one  line above - one line below"
> >
> > I found the most convenient pattern 1 line above and 10 below
> > and I have three pictures, 30 lines total.
> > But it is definitely important that that "one line" is in exactly
> > the same position on all pictures.
> >
> > Alex.
>

   

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