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    Re: Sestrel sextant thoughts?
    From: Antoine Couëtte
    Date: 2020 May 23, 04:17 -0700

    Hello Ned,

    For decades, if not centuries, sextant Manufacturers have been publishing Eccentricity "Calibration" corrections in arc seconds while most generally the verniers show [sub-]arcminutes.

    Why so ? Big mystery to me .

    I suggest that you start sitting down and first make your own curve applicable to your own sextant in tenths of arc minute as a function of Instrument angle. Or better, write down the "border" values inside which the eccentricity remains constant (exactly like the NAL Altitude Corrections).

    I do not know what Bill Morris from New Zealand - our Sextant Expert - would think of such Eccentricity calibration certificate. It seems to go a bit high on one end : nonetheless as long as it stays inferior or equal to 0.1' below 90°, I would not worry too much as I think that this sextant should be ok.

    Your advice here, Bill ?

    The greatest unknown like for any sextant .. has it been dropped onto the ground, or has it been hit by something hard ?

    Shocks can remain totally invisible to the naked eye, and nonetheless they can totally ruin a sextant. In doubt, get it calibrated again.

    Only practice from known places first will show you its real value. After 100 shots, you can start being comfortable with a sextant, or start having firm ground to be cautious ...

    Good luck !

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

       
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