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    Re: SNO-T tests
    From: Ken Gebhart
    Date: 2005 Nov 29, 21:11 -0600

    On 11/28/05 1:09 PM, "Fred Hebard"  wrote:
    > On Nov 28, 2005, at 1:00 PM, Alexandre E Eremenko wrote:
    >>> For instance, the bump at 16
    >>> degrees wasn't
    >>> reproducible between November 13 and November 7.
    >> That's the main problem. If they were reproducible, I'd
    >> make a table of arc correction. But they are not, and I am stilll
    >> at loss whether this has something to do with my observations
    >> or just the sextant is flimsy.
    >> Alex.
    > Alex,
    > My guess would be observational proficiency.  It took me about two
    > years to achieve proficiency in altitude shots with the artificial
    > horizon; I quickly got within 0.5' of arc, but getting well under
    > 0.2' took much longer.  You seem to be pretty close.  Perhaps Frank
    > could comment on how long it took him.
    > Fred
    I have been paying occasional attention to your posts (due to travels), and
    it seems to me that you are neglecting the effect of drum eccentricity.  The
    readings of the micrometer drum itself can be in error by as much as 20 or
    30" of arc all by itself. This is caused by any microscopic deformation of
    the drum shaft, or errors in machining (or damage to) the worm gear. This
    can be added (plus or minus) to any errors determined on the arc.  This will
    pretty much make a mess of any attempts to calibrate the arc unless all
    measurements are made at the same drum reading (not likely when measuring
    stellar distances).
    It seems to me that a way to get a handle on your own drum eccentricity
    might be to measure a moon- star distance over a period of about 2 hours.
    This should give a series of readings over a complete revolution of the
    drum, that could be plotted of graph paper to see what is happening.

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