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    Instumental error?
    From: Alexandre Eremenko
    Date: 2005 Apr 19, 19:59 -0500

    I am still struggling with my SNO-T, trying to determine
    any instrumental error from distances.
    (Once George asked: "Did anyone succeed in determining
    instrumental error of a modern sextant by ordinary observations"?
    I cite from my memory: still cannot manage the search engine
    on this list:-(
    I think I did. My SNO-T sextant has a certifricate, which is
    filled by +10" everywhere on the arc. But even the seller
    confirmed that in the last years of Soviet Union, no one
    really cared to measure and they filled the certificates with
    random numbers (even did not care to vary these numbers:-)
    Anyway, here are the result of my last distance measurements
    as they are. I will appreciate any interpretation of these numbers.
    Index correction. Always from 0 to -0.2', since October 2004.
    I do it every time when I do observations. From the Sun
    or from the stars. The results are consistent.
    All distances I mention are
    measured under
    ideal conditions from my balcony in perfect weather.
    Lunars are reduced with Frank's calculator, star distances with
    my own computer program. A light filter is frequently used on the
    moon at night, an appropriate one on the Sun,
    and no filter on the stars.
    April 19
    2:00 GMT, 8 measurements of Sirius-Procyon,
    standard deviation 0.15', maximal span 0.4',
    distance approx. 25d40' average error +0.5'
    2:20 GMT, 7 measurements of Procyon-Capella,
    stabdard deviation 0.2' maximal span 0.6',
    distance approx. 51d7' average error +0.4'
    Same with Galileo scope, average error +0.3'
    2.37 GMT, 7 measurements of Sirius-Capella,
    standard deviation 0.3' maximal span 0.5'
    distance approx. 65d48', average error +0.6
    22:45 GMT 8 measurements of Jupiter-Saturn,
    standard deviation 0.3', maximal span 0.5'
    distance approx 81d53', average error 0.0'
    23:30 GMT 6 measurements of Sun-Moon distance,
    standard deviation 0.2'
    distance approx 127d10', average error +0.8'
    This is just a sample. My log book is full of similar data,
    and they are consistent in the average,
    produced since October 2004. Can anyone help me to
    interpret this?
    (In the beginning I thought that this is my technique
    to blame, but now (after having tried once Bill's new
    Astra III) I begin to suspect that this is an instrument error.
    a) it is ALWAYS positive.
    b) it ranges from +0.2' to almost 1'.
    c) Sometimes it is almost zero, but rarely.
    Based on the recent observations I can make the following table
    of corrections:
    25      38    51    65    68    71     82    90    127
    -0.5   -0.4  -0.4  -0.6  -0.2  -0.1   -0.2  -0.2  -0.8
    Should I attach this table to my sextant box lid as a
    certificate, and use it?
    Any comments?

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