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    Re: Centring Error Detector
    From: Brad Morris
    Date: 2014 Jan 22, 15:05 -0500

    Frank

    Your idea of using the sextant has been well discussed and does have merit.  The ideal sextant can be set to any arbitrary angle.  All you need is an ideal sextant or one in which all errors are *known*.  Then all of the observed errors can be attributed to the measured sextant. Failing that, the truth remains hidden.  The observed errors will be a hodge podge of errors in the ideal sextant and errors in the measured sextant.

    The beauty of an ultradex is the precision it affords while permitting easy manipulation.  Here's one on eBay right now http://m.ebay.com/itm/191042953903?nav=SEARCH&sbk=1 the top plate and bottom plate engage with a patented interface, that guarantees accuracy and repeatability.  It is an independent NIST traceable, calibrated instrument.  That is something simply not achievable with your sextant concept, attractive as it may be.

    The top and bottom plates of the ultradex  are set parallel to the plane of the sextant.  The beam splitter (or prism or mirror) mounts perpendicularly to that, just like an index mirror.  So rotating the ultradex top plate rotates the horizon optical path. 

    Take a look at this arrangement
    http://www.globalspec.com/reference/14523/160210/chapter-2-2-beam-splitter.

    In place of the collimator put the sextant to be measured.  In place of the mirror 1, is the horizon path disturbed. In place of mirror 2 is the horizon path, undisturbed.

    Perhaps this will engender a more meaningful response

    Brad

    On Jan 22, 2014 1:33 PM, "Frank Reed" <FrankReed{at}historicalatlas.com> wrote:

    Brad, you wrote:

    "If you followed that, then you know this is awesome in comparison to the Kew certificates. I just haven't figured out how to align the beam splitter plate to zero"

    You can do that with any room-temperature superconducting photonic matrix. Or so they say...

    -FER

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