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    Re: Finding IC for A-12 bubble sextants
    From: David Pike
    Date: 2021 Oct 8, 14:48 -0700

    Art Leung you wrote:  I am still learning how to best manage the centering of the object in the bubble.

    You and me both for the A12.  You might like to try a technique I’ve found useful when calibrating my periscopic sextants.  These all have graticules rather than bubbles, and I’m not sure if it would work for a bubble.  After a few minutes you get a feel for the rate the body is moving across the eyepiece, up and right, or down and right.  Then, if the graticule is central and within the tramlines but the body is still a fraction off, I don’t try to move it into the centre of the graticule and risk upsetting everything; I simply wait until the body climbs to the centre of the graticule by itself and either note the time if I’m doing the maths manually or hit 'Pause' on GPS Anti Spoof if the App is doing the work.  This only works in a static situation of course.  In the air, the body and graticule assume lives of their own.  Hence the need for a mechanical averager.  DaveP

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