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    Re: Sestrel sextant thoughts?
    From: Antoine Couëtte
    Date: 2020 May 24, 00:18 -0700

    Dear Alexander,

    Thank you for your kind and clear explanation.

    It is definitely the right one, especially since you saw it in use for your own sextant.

    In order to "store" the original eccentricity correction data, standard procedures have always been excellent to print and retain them in the sextant boxes as registered certificates. 

    No question about that.

    Still, we can very easily go a bit further, and it seems worth elaborating a little further.

    It has always struck me that, with very little extra work, one can very easily work out an "eccentricity correction curve" exactly like we find "deviation [correction] curves" carefully [hand] drafted for [hopefully] all magnetic compasses.

    The general shape of the magnetic compasses deviation curves is well known thanks to M. Archibald Smith's compensation method, which by the way is exactly a [first and] second order Fourier's series approximation.

    Likewise the general shape of a sextant eccentricity "perfect" deviation curve is well known and it can be reconstructed from a set of such recorded data. Hence it is possible to build a smooth "eccentricity correction curve in tenths of arc-minute" immediately usable for any sextant.

    Hence easily achievable "added-on extra values" for the Sextant Manufacturers would be deriving such eccentricity correction curves in tenths of arc minute to be immediately usable, i.e. "operational".

    Maybe it is a little late nowadays to have such a wish here at the age of GPS, Glonass, Galileo, ... as almost all the Celnav Fairies seem to have definitely vanished.

    Best Regards,

      Kermit - antoine.m.couette[at]club-internet.fr 

       
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