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On Nov 27, 2006, at 12:21 AM, FrankReedCT@aol.com wrote:

> George, regarding getting a position fix by lunar distances at
> known GMT,
> you wrote:
> ....
> "He has claimed that a skilled observer can measure lunar distances
> reliably to 0.1 arc-minutes; claims which have been treated with
> scepticism by some contributors, me included."
>
> Just so we're clear here, what I claim is that a moderately careful
> observer with a well-adjusted metal sextant, equipped with a good
> telescope, who shoots four lunar distances in a row will find a
> standard deviation accuracy of about 0.2 minutes of arc. And when
> you average four of them, the standard deviation of the resulting
> combined observation is just about 0.1 minutes of arc, repeatedly
> and reliably. That's hardly a radical claim.

Frank,

The most thorough study of this was reported by Jan Kalivado a few
years ago, from a German paper of the 1870s or so.  As I recall, the
standard deviation was around 0.25 to 0.3 minutes of arc.  So the
standard error of the mean of four observations would be about 0.15
minutes of arc rather than the 0.1 you claim.  That's pretty good
though.

Fred

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