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    Re: Finding IC for A-12 bubble sextants
    From: Matus Tejiscak
    Date: 2021 Oct 9, 13:53 -0700

    Dear Ed,

    others already gave a lot of very useful advice. What I haven't seen mentioned yet is that I observe a different IE when looking at the reflected image of the Sun than when looking through the index glass at a star. The difference is about +13' for the Sun vs. about +20' for the stars. I'd recommend to measure the IE through the index glass as well.

    My method is to take a sequence of sights from a tripod and calculate the St Hilaire intercept for each sight from my known position, which amounts to direct IE measurement. Then I use statistics to determine the IE from this collection of IE samples. That's where things get tricky, as I seem to get a multimodal distribution of errors -- even when adjusting the angle in only one direction to eliminate the difference in backlash -- so I'm still in the process of figuring out what else could affect this.


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