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>> Alex has in the past looked poorly on natural horizon IE/IC.
>
> 1. Natural horizon is rarely so well defined as
> a star or a Sun's edge.
> 2. The Russian book "Precision of astronomical observations"
> says that (based on large statistics) IC from horizon is much less
> precise than that from the Sun.

I'm sure the author of the study had performed more trials than I have, but
the standard deviation (n-1) of my natural horizon IE checks--from a
boat--are every bit as good as those of the sun from a chair.

They do help to verify that my vertical sun IE checks (I believe due to
astigmatisms) are too high.  Currently on the arc 0.75' on for sun,
0.3'natural on for horizon.  This syncs up with vertical sun IE checks done
with glasses.

I have confirmed this by standing on the Soldier's Home Road overpass (over
Sagamore Parkway) looking east and using flat-top buildings, corn-refinery
stacks and towers as well as the distant tree line.  A bit closer than I
would like, but it should not cause more than a 0.1' error.

It would appear that a good bit of the problems I have with consistent
undershoots is using a sun-determined IC that is too high.
>
>> You have noted in the past that a bit of side error may be useful
>
> Later Frank corrected this statement. It can be useful for IC
> checks with stars. But it is certainly harmful with Sun or Moon
> checks.

Understood, especially with your 4SD requirements.

Bill


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