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Alex wrote

> It remains to explain why star and Sun tests give
> consistently
> smaller IC than the Moon test (at least in my measurements).
> It is interesting how various authors rate the
> various tests
> for IC in the order of decreasing precision.
>
> Heath (of Hezzanith): Star, Horizon, Sun.
> Russian manual: Sun and Star equally good, then Horizon.
> (They quote the statistics that the typical
> accuracy of the Sun/star test is 0.1 to 0.2, while
> the Horizon gives only 0.5.

I surmise it eventually becomes a one-man-dog.  What works for one person
may not work for another human being.  I am horrible at one star IE checks.
Good sun IE checks usually have a sigma equal to the horizon IE checks, but
the values vary due to (I firmly believe) problems with astigmatism with my
naked eye.

As an undergrad psych major I can prove that input is usually a long way
from final perception.  That includes classes and labs on the optical
system.

I do agree with your assessment of moon IE checks.  I feel it is both a
harder target in terms of edge definition and axis, as well as a challenge
to my astigmatism.  I can measure horizontal vs. vertical sun differences,
but have no clue what is happening when I tilt the sextant to do a moon IE
check.

Bill




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