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    Re: Experience of using a hand-held bubble sextant in a light aircraft
    From: Tracy Shrier
    Date: 2019 Sep 29, 19:14 -0700

    Well Done Geoffrey! Nothing more fun than than trying to get a good fix in the air!!

    4 years into my adventures with the A12 I would amplify your realization of the need to average. Weems specifically built the A12 to this need. Take the standard 2 minute sight, trigger an elevation every 10-15 seconds, read your median mark on the index drum as Hs, and don't second guess the outliers that you triggered, it's all good data.

    Did you attempt to correct for refraction through the windows? I use the "Standard Dome" table to some avail. But I am convinced that not knowing the refraction of the windows I sight through, particularly when having to sight at oblique angles through the windows, causes significant errors in my sights. My Sep 9 post shows a great fix with sights taken a moderate elevations and generally perpendicular through the windows. Attached is my most recent, a Sun-Moon fix on the 20th. My sun sight was straight out my left window and the resulting LOP grazes my FMS location by maybe 6nm. I took the moon sight diagonally accross the cockpit through the left windshield, at an angle easily less than 50° through the glass. The resulting LOP is 30 some miles at it 's closest to my FMS. All else being equal I think window refraction is the differnce between the two fixes.

    Tracy

    File:
    CelNav20092019-Hsdata.pdf
    File:
    CelNav20092019-plot.pdf
    File:
    CelNav20092019-reduction.pdf
       
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