# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: star-to-star distances
From: Alexandre Eremenko
Date: 2004 Sep 30, 18:38 -0500

```Dear Fred,

On Thu, 30 Sep 2004, Fred Hebard wrote:

> It's only recently that my
> standard deviations have started coming in consistently under 0.2'

As a mathematician, I don't like the standard deviation
for suich small samples.

What I do with multiple observations is this:
1) first I plot the measured altitudes against time
and see whether the dots are on the straight line.
Usually most of the points fit a straight line well,
with one, sometimes two relatively much off.

Those which are clearly off the line should be discarded.
They can be off only because of some mistake in the
measurement or recording.

The rest I average and then reduce the average.
I mean this is what I would do in a "practical situation".

In my current experiments, I reduce all observations,
(except those rejected). Then obtain the average deviation,
and for each observation compute the difference
between the deviation derived from this observation and
the average deviation.

Then I consider the MAXIMAL difference as a measure of
quality of my measurement.

Something like this is recommended in several books.

> to set the arc
> slightly different from the final contact point, then wait for the
> object to settle on the contact point.

Yes, this I also do. So far I see no noticeable difference
in the results
between "bringing in contact" and "waiting for contact".

> You can wait with stop watch in
> hand and click it at the moment of contact.

I don't like this because then I have to reset the stopwatch
for each observation. (besides, I do not have a stopwatch:-)
At the moment
of contact,
I say "Yes!" to myself (aloud) then quietly turn my face
from the sextant to the watch, and look at the seconds first.
Then I subtract one second (needed to say "Yes!" and turn my face).
And record seconds first, then minutes then hour.

> to record to the tenth of a second, which I haven't done thus far.

Do you really think this may have any influence on your
result? Let us count: 0.1sec=1.5"=0.025' and we agreed that
a sextant scale can be read only up to 0.1'.
So it seems that the tenths of a second are irrelevant.

The Russian manual recommends to record the time to 0.5
of a second
though:-)

> is that 30mm is good with a 6x scope and 35mm for a 7x scope,

Actually there is an interesting point here.
In this SNO-T certificate, it is written that the inverting
scope has magnification "6 OR 7".
I am not sure how to interpret this: they had two different
models of scopes, or they did not care to measure magnification
precisely:-)

> Perhaps we can meet sometime at Purdue
> when I go to see my daughter;
> I'll bring my sextant.

Oh, really?!! Don't forget to warn me by e-mail in advance
so that I will give you my phone numbers!

Alex.

```
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