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Interesting concept. I am still trying to wrap my mind around it to see
if there are any flaws. It appears to make sense to me.

Nevertheless, the question remains, how does one apply the rest of the
correction. One text suggests "applying the correction until the sextant
can be adjusted" but does not tell the reader 1.) how this difference is
to be applied and 2) what adjustments must be made to the sextant.

Every time I reach a point where I think I have it all figured out
another glitch appears to take the wind out of my sails.

Robert

P.S. I should mention that backlash is not a factor here: it is my
practice to rotate the verier drum in the same direction; always. Even
the finest sextants have a bit of backlash.

>I don't think you should be performing this step:
> 62.6 - 0.7 = 61.9
>
>You observed two diameters.  Let's correct each of them
>separately for the derived index error:
>  32.0 - 0.7 = 31.3
>  30.6 + 0.7 = 31.3
>Therefore your measurements say twice the diameter is 62.6,
>which is the same as you get by simply adding the two raw
>observations together.
>Thus, your measured semidiameter is 15.65 -- a bit closer,
>but still not exact.
>
>If you measure the SD to be too small, it could be explained
>by flattening due to refraction.  Basically, the altitude of
>the lower limb is less than the altitude of the upper limb,
>so their refraction corrections would be different.  But the
>difference should be no more than 0.05' for reasonable altitudes.
>
>If you measure the SD to be too large, it could be explained
>by the illusion that brighter objects appear larger -- is this
>called illumination?
>
>        -- Bill
>

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