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re halftant / puptent (David Weilacher):

> Problem is that in the afternoon, the limb that I am bring down is
> the upper limb, refraction wise, but appears as lower limb against
> east horizon through the eyepiece of my puptent.

Agreed.

> Our marine almanac combines semidiameter and refraction together as
> one figure.  Thats what makes our lower and upper limb corrections
different.

Agreed.  But the Almanac doesn't provide corrections for Hs greater
than 90 degrees, so you can't use it directly in the afternoon anyway.

Once you correct for dip and index error, and then subtract from
90 degrees, the result is exactly what you would have gotten if you
had measured the upper limb against the western horizon (assuming
today's
dip matches the tables, of course).  From this result, you need to
adjust for semidiameter and refraction, and the upper limb table entry
is correct for both.

There would indeed be a problem if you tried to apply either or both
of semidiameter / refraction corrections *before* subtracting from 180.
If there's a problem I don't see, can you demonstrate it with numbers?
        -- Bill

   

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