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    Re: Calibrating a Bris sextant
    From: Greg Rudzinski
    Date: 2017 Aug 13, 13:08 -0700

    Marty,

    If a lower limb Sun is timed on a Bris sextant image then subtract S.D. and add dip & refraction to the calculated Hc . This gives the Hs calibration.  Do not attempt to use a sight reduction table (pub. 229, 249) for this which uses a selected assumed position. Much better to use a navigation computor, usno, or smart phone app with the GPS position as the assumed position.

    Give me all your data and I can help generate a calibration diagram for your Bris. Needed: Date, UT time, GPS position, height of eye, Sun limb used ( upper, lower, center ).

    Double check the calibration by using a standard sextant to make an observation right after the Bris observation. The Hs readings should be within 3' or 4' difference. Better yet have an assistant with a sextant take a reading on your mark using the Bris.

    Greg Rudzinski

       
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