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    Re: Star-star distances for arc error
    From: Bill B
    Date: 2009 Jun 24, 05:37 -0400

    Douglas wrote:
    > I've done this. It provides a method of checking a sextant but is not easy
    > accuracy unless you have some clamping system to hold the sextant still and be
    > able to rotate the sextant into alignment.
    I have any number of photographic tripods and clamping (grip) systems. They
    are great for determining if a measured semi diameter is off due to frame
    flex or astigmatism.  Great for calibrating a practice bubble horizon at LAN
    from a known latitude.  Terrible for star-to-star distances.
    While some can use one star for index error/index correction I cannot. I
    just can't see it within a minute of an arc.  However, as pointed out with
    star-to-star one has the advantage of swinging the two across each other
    (much easier to align IMHO) as well as two different magnitudes and quite
    often two different colors.
    As an analogy, you can take the finest rifle and scope available, bench
    mount the pair and bore sight them for a given range, then add the
    match-grade ammo of your choice into the equation and dynamically test the
    system--then adjust.  All that does is give you advantage in the field. Once
    you take it off the bench, the skill of the operator to hold it steady and
    adjust for recoil, muzzle flip, elevation and windage makes all the
    Just a thought--or two.
    Bill B.
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